Negative resist composition, method for the formation of resist patterns and process for the production of electronic devices

ABSTRACT

The negative resist composition comprises (1) a film-forming polymer which is itself soluble in basic aqueous solutions, and contains a first monomer unit with an alkali-soluble group in the molecule and a second monomer unit with an alcohol structure on the side chain which is capable of reacting with the alkali-soluble group, and (2) a photo acid generator which, when decomposed by absorption of image-forming radiation, is capable of generating an acid that can induce reaction between the alcohol structure of the second monomer unit and the alkali-soluble group of the first monomer unit, or protect the alkali-soluble group of the first monomer unit. The resist composition can form intricate negative resist patterns with practical sensitivity and no swelling.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims priority of JapanesePatent Applications Nos. Hei 11-248619, Hei 11-260815, 2000-61090,2000-61091, and 2000-257661, all filed, the contents being incorporatedherein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a resist composition, and morespecifically it relates to a chemical amplification resist compositionthat can be developed by a basic aqueous solution after exposure. Theinvention further relates to a negative resist pattern forming methodemploying the resist composition. The resist composition of theinvention can be used to form intricate negative resist patterns thathave practical sensitivity without swelling. Furthermore, the presentinvention relates to electronic devices including semiconductor devicessuch as LSI and VLSI and magnetic recording heads such as MR heads, andthe production process thereof.

[0004] 2. Description of the Related Art

[0005] Higher integration of semiconductor integrated circuits hasprogressed to the current situation in which LSIs and VLSIs arefeasible, and the minimal wiring widths of wiring patterns have reachedthe range of 0.2 μm and smaller. This has rendered essential theestablishment of microworking techniques, and in the field oflithography the demand has largely been met by shifting the ultravioletwavelengths of light exposure sources to shorter wavelengths in the farultraviolet range; it has been predicted that light exposure techniquesemploying light sources with wavelengths in the deep ultraviolet rangewill soon be implemented in mass production processes. At the same time,development has been rapidly progressing with resist materials thatexhibit lower light absorption of the aforementioned shorterwavelengths, have satisfactory sensitivity and also exhibit high dryetching resistance.

[0006] In recent years much research has been conducted in the field ofphotolithography employing as the exposure light sources kryptonfluoride excimer lasers (wavelength: 248 nm, hereunder abbreviated toKrF), as a new light exposure technique for manufacture of semiconductordevices, and they are being widely used for mass production. H. Ito etal. of IBM, U.S.A. have already developed resist compositions based onthe concept of “chemical amplification”, as resists with highsensitivity and high resolution that are suitable for such shortwavelength light exposure. (See, for example, J. M. J. Frechet et al.,Proc. Microcircuit Eng., 260(1982), H. Ito et al., Digest of TechnicalPapers of 1982 Symposium on VLSI Technology, 86(1983), H. Ito et al.,“Polymers in Electronics”, ACS Symposium Series 242, T. Davidson ed.,ACS, 11(1984), and U.S. Pat. No. 4,491,628). As is readily understoodfrom these publications, the fundamental concept of chemicalamplification resist compositions is based on higher sensitivity throughan improved apparent quantum yield achieved by a catalytic reaction inthe resist film.

[0007] There may be cited the very widely used and researched chemicalamplification resist type that comprises t-butoxycarbonylpolyvinylphenol (t-BOCPVP) and further contains a Photo Acid Generator(PAG), which has the function of generating an acid upon light exposure;“post exposure baking” (PEB) of the exposed sections of the resistresults in loss of the t-BOC groups to give isobutene and carbondioxide. The proton acid produced upon loss of t-BOC serves as acatalyst promoting a deprotection chain reaction, which greatly altersthe polarity of the exposed sections. With this type of resist, anappropriate developer can be selected to match the large change inpolarity of the exposed sections, to easily form an intricate resistpattern with no swelling.

[0008] Incidentally, one of the high-resolution techniques widely usedin recent years is a method employing a mask that alters the phase oflight, known as a phase-shift mask or Levenson mask, and it holdspromise as a method that can give resolution below the exposure lightwavelength and an adequate focal depth. When such masks are used,negative resists are usually appropriate due to restrictions of the maskpattern, and this has created a strong demand for provision of negativeresists. When KrF is used as the light source, these masks areconsidered for applications in which resolution of under 0.20 μm isrequired, and this has led to spurring development of high performanceresists that can resolve intricate patterns without swelling, asmentioned above. There has also been abundant research in the field oflithography using argon fluoride excimer lasers (wavelength: 193 nm,hereunder abbreviated to ArF) and electron beam (EB) sources, with evenshorter wavelengths than KrF, and it is an essential technique forformation of patterns of less than 0.13 μm. The development of anegative resist that can be used for ArF, EB and the like on which moreadvanced microworking depends, will therefore provide many industrialadvantages.

[0009] Alkali-developable negative resists for KrF and EB include thosebased on polar reaction caused by an acid-catalyzed reaction [forexample, H. Ito et al., Proc. SPIE, 1466, 408(1991), S. Uchino et al.,J. Photopolym. Sci. Technol., 11(4), 553-564(1998), etc.] and thosebased on acid catalyzed crosslinking reaction [for example, J. W.Thackeray et al., Proc. SPIE, 1086, 34(1989), M. T. Allen et al., J.Photopolym. Sci. Technol., 7, 4(3), 379-387(1991), Liu H. I., J. Vac.Sci. Technol., B6, 379(1988), etc.]. Crosslinkable types of negativeresists for ArF are also known [for example, A. Katsuyama et al.,Abstracted Papers of Third International Symposium on 193 nmLithography, 51(1997), K. Maeda et al., J. Photopolym. Sci. Technol.,11(4), 507-512(1998), etc.]

[0010] However, despite the strong demand for a high performancenegative resist that can be used for high resolution techniquesemploying the aforementioned phase-shift masks or Levenson masks andthat can be applied for KrF, ArF and EB, the existing negative resiststhat are practical for use consist of only the crosslinkable typesmentioned above. Crosslinkable negative resists accomplish patterning byutilizing a crosslinking reaction to increase the molecular weight atthe exposed sections, thus producing a difference in solubility in thedeveloping solution with respect to the unexposed sections; it istherefore difficult to increase contrast, and unlike resists based onpolar reaction caused by an acid-catalyzed reaction, it is impossible tocircumvent the limitations on microworking due to pattern swelling.

[0011] As described above, when negative chemical amplification resistsare examined, they are found to be largely classified as types thatcontain in the resist an alkali-soluble base resin, a photoacidgenerator that decomposes upon absorption of image-forming radiation torelease an acid and a substance that causes a polarity change due to theacid-catalyzed reaction, and types that contain in the resin analkali-soluble base resin, a photoacid generator that decomposes uponabsorption of image-forming radiation to release an acid and a substancethat can cause crosslinking reaction within the resin. The formerchemical amplification resists that utilize a polar reaction typicallymake use of a pinacol transfer reaction as disclosed, for example, in R.Sooriyakumaran et al., SPIE, 1466, 419(1991) and S. Uchino et al., SPIE,1466, 429(1991). The acid-catalyzed reaction in such a resist proceedsin the following manner.

[0012] That is, the alkali-soluble pinacol is affected by the acid andheat, being rendered alkali-insoluble. However, such chemicalamplification resists have a problem in terms of resolution. Althoughthe pinacol itself is rendered alkali-insoluble by the acid-catalyzedreaction as explained above, the alkali-soluble base resin itself doesnot react and it is therefore impossible to achieve a sufficientdissolution rate difference.

[0013] Chemical amplification resists are also disclosed in JapaneseUnexamined Patent Publications (Kokai) Nos. 4-165359, 7-104473,11-133606, and elsewhere. For example, Japanese Unexamined PatentPublication (Kokai) No. 4-165359 discloses a radiation-sensitivecomposition characterized by containing an alkali-soluble polymercompound, a secondary or tertiary alcohol with a hydroxyl group on acarbon directly bonded to an aromatic ring, and an acid precursor thatgenerates an acid upon radiation exposure. The secondary or tertiaryalcohol used here may be, for example, a phenylmethanol derivativerepresented by the following formula.

[0014] where A represents an alkyl or methylol group of no more than 4carbons.

[0015] where R₄ and R₅ may be the same or different, and each representsa hydrogen atom or a phenyl group. The acid-catalyzed reaction in theresist proceeds in the following fashion.

[0016] As mentioned above, the alkali-soluble polymer compound isaffected by the acid and heat so that the secondary or tertiary alcoholforms a dehydration bond, thus becoming alkali-insoluble. However,because an aromatic ring is included in the secondary or tertiaryalcohol that contributes to the acid-catalyzed reaction, although itspresence in the chemical amplification resist is believed to be forimproved etching resistance, this raises the problem of restrictions onthe exposure light source. This is because the aromatic ring has highlight absorption and is therefore particularly unsuitable forapplication to short wavelength KrF lasers and ArF lasers (argonfluoride excimer laser: wavelength: 193 nm). The other purpose of thearomatic ring is thought to be conjugated stabilization of the doublebond produced by dehydration, but the hydroxyl group is bonded to thecarbon directly bonded to the aromatic ring. With this structure, thedehydration in the alcohol molecule constitutes the primary reactionwhereas reaction does not occur with the polar groups (phenolic hydroxylgroup, etc.) of the base resin, such that the intended polar change isreduced. Furthermore, since no double bond is produced by dehydrationwith a primary alcohol, the use is limited to a secondary or tertiaryalcohol, and it is desirable to eliminate this restriction in order toallow a wider scope of application.

[0017] Chemical amplification resists utilizing the latteracid-catalyzed crosslinking reaction typically make use of crosslinkingreaction of an alkali-soluble resin with a melamine-based crosslinkingagent such as methoxymethylol melamine, and such are disclosed, forexample, in M. T. Allen et al., J. Photopolym. Sci. Technol., 7, 4(3),379-387(1991). The crosslinking reaction in the resist proceeds in thefollowing fashion.

[0018] The use of a melamine-based crosslinking agent such as in thistype of chemical amplification resist can provide an effect of loweralkali solubility through gelling reaction of the base resin (increasedmolecular weight by crosslinking of the resin) and throughdepolarization of the resin polar groups (phenolic hydroxyl groups) as aresult of the crosslinking. However, the methoxymethylol melamine usedhere as the crosslinking agent inherently has low polarity, andtherefore a sufficient dissolution rate difference cannot be produced.It is desirable to provide a resist that has high polarity of the resinand additives prior to light exposure, and low polarity of the resin andadditives after light exposure.

SUMMARY OF THE INVENTION

[0019] The present invention is directed to overcome the aforementionedprior art problems.

[0020] In one aspect thereof, the present invention is directed toprovide a novel resist composition that allows the use of basic aqueoussolutions (standard alkali developers) as the developers, that havepractical sensitivity and that can form intricate negative resistpatterns with no swelling.

[0021] It is another object of the invention to provide a novel resistcomposition that is suitable for deep ultraviolet image-formingradiation, typical of which are KrF and ArF excimer lasers, as well aselectron beams, and that also has excellent dry etching resistance.

[0022] It is yet another object of the invention to provide a novelresist composition that gives a high polarity difference between theexposed sections and unexposed sections, to form intricate patterns withhigh sensitivity, high contrast and high resolution.

[0023] It is still another object of the invention to provide a resistpattern forming method that employs the novel resist composition.

[0024] In another aspect, it is an object of the present invention toovercome the aforementioned problems associated with the prior arttechniques by providing a resist composition that has a largedissolution rate difference between the exposed sections and unexposedsections, to allow formation of intricate patterns with highsensitivity, high contrast and high resolution.

[0025] It is another object of the invention to provide a resistcomposition that allows the use of basic aqueous solutions (standardalkali developers) as the developers.

[0026] It is yet another object of the invention to provide a resistcomposition that is suitable for deep ultraviolet image-formingradiation, typical of which are KrF and ArF excimer lasers, as well aselectron beams, and that also has excellent dry etching resistance.

[0027] It is still yet another object of the invention to provide aresist pattern forming method employing a resist composition accordingto the invention.

[0028] In still another aspect, one object of the present invention isto provide a novel negative resist composition free of the problem ofpattern swelling and capable of forming a fine pattern with practicallyusable sensitivity using a short wavelength light source for exposure.The object of the present invention includes providing a novel resistcomposition capable of coping with an exposure light source in the deepultraviolet region, represented by KrF or ArF excimer laser, and havingexcellent dry etching resistance. The object of the present inventionfurther includes providing a novel resist composition capable of greatlydifferentiating the polarity between the exposed area and the unexposedarea and thereby forming a fine pattern favored with all of highsensitivity, high contrast and high resolution.

[0029] Another object of the present invention is to provide a methodfor forming a resist pattern using the above-described resistcomposition.

[0030] In addition to the above problems, there is another problem to besolved by the present invention.

[0031] The present inventors have already proposed in Japanese PatentApplication No. 11-260815 a novel polarity-changing, high-performancenegative resist composition as a resist that can meet the demandsdescribed above. The proposed resist composition employs an alicyclicalcohol, and preferably a tertiary alcohol with a stereochemically fixedstructure, as the alkali-insolubilizing additive. The resist compositioncan form an intricate negative resist pattern with a larger polaritydifference between the exposed and unexposed sections and highersensitivity, contrast and resolution compared to conventional resists,by the reaction shown in formula (13) below, for example.

[0032] As a result of more diligent research on the aforementionednegative resists, the present inventors have completed the presentinvention upon determining the most suitable conditions for obtainingresist patterns with high sensitivity and high resolution.

[0033] That is, the present invention has been completed upon findingthat it is possible to provide a negative resist composition with evenhigher sensitivity and higher resolution by setting numerical limits onthe molecular weight distribution of the base resin used according tothe first aspect of the invention, and by limiting the range for themolecular weight of the base resin used according to the second aspect.

[0034] It is therefore one object of the invention to provide a novelnegative resist composition with vastly improved sensitivity andresolution.

[0035] It is another object to provide a negative resist pattern formingmethod employing the novel negative resist composition.

[0036] Further, the present invention has an object to provide a processfor the production of electronic devices using novel negative resistcomposition of the present invention, and electronic devices producedupon application of such production process.

[0037] The above objects and other objects of the present invention willbe appreciated from the following descriptions of the present inventionreferring to preferred embodiments thereof.

FIRST INVENTION

[0038] As a result of diligent research aimed at achieving the objectsin the first aspect of the present invention, the present inventors havecompleted the present invention upon discovering that for chemicalamplification resist compositions, it is important to use as the baseresin a film-forming polymer which has an alkali-soluble group in themolecule and is soluble in basic aqueous solutions, and to include inthe polymer a monomer unit with an alcohol structure, preferably atertiary alcohol structure, on the side chain. When the photo acidgenerator used in combination with the film-forming polymer in theresist composition of the invention absorbs image-forming radiation anddecomposes, it produces an acid which either induces reaction betweenthe alcohol structure on the side chain of the monomer unit in thepolymer and the portion of the same polymer with the alkali solublegroup, or else protects the alkali-soluble group. As a result, theexposed sections that have absorbed the image-forming radiation arerendered alkali-insoluble, allowing formation of a negative resistpattern.

[0039] The present invention (first invention) resides in a negativeresist composition which is developable in basic solutions,characterized by comprising

[0040] (1) a film-forming polymer which is itself soluble in basicaqueous solutions, and contains a first monomer unit with analkali-soluble group and a second monomer unit with an alcohol structurecapable of reacting with the alkali-soluble group, and

[0041] (2) a photo acid generator which, when decomposed by absorptionof image-forming radiation, is capable of generating an acid that caninduce reaction between the alcohol structure of the second monomer unitand the alkali-soluble group of the first monomer unit, or protect thealkali-soluble group of the first monomer unit, and by being itselfsoluble in basic aqueous solutions, but upon exposure to theimage-forming radiation being rendered insoluble in basic aqueoussolutions at its exposed sections as a result of the action of the photoacid generator.

[0042] In another aspect of the present invention, the present inventionresides in a negative resist pattern forming method, characterized bycomprising the following steps:

[0043] coating a negative resist composition of the invention onto atarget substrate,

[0044] selectively exposing the formed resist film to image-formingradiation that can induce decomposition of the photo acid generator ofthe resist composition, and

[0045] developing the exposed resist film with a basic aqueous solution.

SECOND INVENTION

[0046] As a result of diligent research aimed at achieving the objectsin the second aspect of the present invention, the present inventorshave completed the present invention upon discovering that for chemicalamplification resist compositions, it is effective to include, inaddition to a base resin composed of an alkali-soluble polymer and aphotoacid generator capable of decomposing upon absorption ofimage-forming radiation to generate an acid, also an alicyclic alcohol,and especially a tertiary alcohol with a stereochemically fixedstructure, as an additive that can render the resist alkali-insoluble.

[0047] The present invention (second invention) therefore provides anegative resist composition characterized by comprising a combination ofthe following reaction components:

[0048] (1) a base resin composed of an alkali-soluble polymer,

[0049] (2) a photoacid generator capable of decomposing upon absorptionof image-forming radiation to generate an acid, and

[0050] (3) an alicyclic alcohol with a reactive site that can undergodehydration bonding reaction with the polymer of the base resin in thepresence of the acid generated by the photoacid generator.

[0051] The present invention also provides a negative resist patternforming method, characterized by comprising the following steps:

[0052] coating a negative resist composition according to the inventiononto a target substrate,

[0053] selectively exposing the formed resist film to image-formingradiation that can induce decomposition of the photoacid generator ofsaid resist composition, and

[0054] developing said resist film with a basic aqueous solution afterpost exposure baking.

[0055] The resist composition of the invention encompasses, as apreferred mode in addition to the description in the claims, a negativeresist composition characterized in that the base resin is aphenol-based polymer, a (meth)acrylate-based polymer or a mixturethereof.

THIRD INVENTION

[0056] As a result of extensive investigations to solve theabove-described problems in the third aspect of the present invention,the present inventors have found that for the chemically amplifiedresist composition, the matter of importance is to use a film-formingfirst polymer having an alkali-soluble group and being soluble in abasic aqueous solution as the base resin and at the same time to containa second polymer having an alcohol structure on the side chain in theresist composition. The present invention has been accomplished based onthis finding.

[0057] More specifically, the above-described object of the presentinvention can be attained, by a negative resist composition comprising afirst polymer having an alkali-soluble group, a second polymer having onthe side chain an alcohol structure capable of reacting with thealkali-soluble group, and a photoacid generator capable of generating anacid which decomposes by absorbing a radiation for forming an image andexcites a reaction between the alkali-soluble group of the first polymerand the alcohol of the second polymer, wherein the composition itself issoluble in a basic aqueous solution and upon exposure to the radiationfor forming an image, the exposed area becomes insoluble in the basicaqueous solution under the action of the photoacid generator.

[0058] According to the present invention, when the negative resistcomposition is exposed to a radiation for forming an image, thephotoacid generator generates an acid capable of exciting an reactionbetween the alkali-soluble group of the first polymer and the alcohol ofthe second polymer, as a result, an acid catalytic reaction takes place,whereby the exposed area can be insolubilized in a basic aqueoussolution.

[0059] Furthermore, in the negative resist composition of the presentinvention, the reaction excited by the photoacid generator can be aprotection-type reaction of protecting the alkali-soluble group and/oran insolubility promotion-type reaction of promoting theinsolubilization of the alkali-soluble group in a basic aqueoussolution.

[0060] Upon reaction of the alcohol with the alkali-soluble group of thefirst polymer, the reaction site of the alcohol forms an ether bond, anester bond or the like to protect the alkali-soluble group of the firstpolymer and thereby insolubilize the alkali-soluble group in a basicaqueous solution. As a result, a great difference arises in the polaritybetween the unexposed area and the exposed area. By virtue of this, thenegative resist composition can be free of the problem that the exposedarea swells, and favored with all of high sensitivity, high contrast andhigh resolution.

[0061] Accompanying the above-described protection-type reaction, analkali insolubility promotion-type reaction of diminishing the propertyof the alkali-soluble group in the first polymer may be allowed toproceed. In this case, the difference in the solubility from theunexposed area increases, therefore, a negative fine resist pattern canbe similarly formed.

[0062] Furthermore, in the negative resist composition of the presentinvention, the alcohol structure is preferably a tertiary alcoholstructure. When the second polymer contains a tertiary alcohol structureon the side chain, a dehydration reaction readily takes place with thealkali-soluble group of the first polymer and the reaction between thefirst polymer and the second polymer can be accelerated.

[0063] In addition, in the negative resist composition of the presentinvention, the tertiary alcohol structure may be a structure representedby any one of the following formulae (1) to (4):

[0064] wherein R represents an atomic group connected to the main chainof the second polymer and R₁ and R₂ each is an arbitrary alkyl grouphaving from 1 to 8 carbon atoms containing a linear or branchedstructure or a cyclic structure;

[0065] wherein R has the same meaning as defined above, n is a number of2 to 9 and R_(x) is a group having from 1 to 8 carbon atoms containing alinear or branched structure or a cyclic structure;

[0066] wherein R has the same meaning as defined above, Y representshydrogen atom or an arbitrary alkyl group having from 1 to 6 carbonatoms, an alkoxycarbonyl group, a ketone group, a hydroxyl group or acyano group;

[0067] wherein R and Y each has the same meaning as defined above.

[0068] The tertiary alcohol having the structure shown above canundertake the reaction of insolubilizing the alkali-soluble group of thefirst polymer in the presence of an acid generated from the photoacidgenerator and thereby more surely insolubilize the exposed area in abasic aqueous solution.

[0069] It is sufficient if the second polymer has compatibility with thefirst polymer, and the first polymer and the second polymer each is notparticularly limited on the main chain moiety thereof. However, in thenegative resist composition of the present invention, the first polymerand the second polymer each may comprise at least one monomer unitselected from the group consisting of acrylic acid-type, methacrylicacid-type, itaconic acid-type, vinylbenzoic acid-type, vinylphenol-type,bicyclo[2.2.1]hept-5-ene-2-carboxylic acid-type and N-substitutedmaleimide-type compounds and derivatives thereof. The monomer unit ofthe first polymer and the monomer unit of the second polymer may be thesame or different. Each polymer may be formed of a single monomer or maybe in the form of a copolymer.

[0070] In the first polymer as the base resin, the ratio occupied by themonomer unit having an alkali-soluble group is not limited as long asthe resin itself shows appropriate alkali solubility, however, it isnecessary to take account of obtaining an appropriate alkali solubilityspeed which is considered practicable as the negative resist (in a 2.38%TMAH developer, a solubility speed of approximately 100 to 30,000 Å/s).If such an alkali solubility speed is satisfied, a homopolymercomprising one component monomer unit may be used as the alkali-solublebase resin and this composition is preferred. Examples of such a resininclude polyvinyl phenol, polyvinylbenzoic acid, polymethacrylic acidand polyacrylic acid.

[0071] In the case where the polymer comprises a monomer unit consistingof two or more components and the alkali-soluble group is a carboxylgroup, the monomer unit content is preferably from 10 to 90 mol %, morepreferably from 30 to 70 mol %. If the monomer unit content is less than1 mol %, the alkali solubility is insufficient and the patterning cannotbe satisfactorily performed, whereas if it exceeds 90 mol %, the alkalisolubility is too strong and the dissolution in a basic aqueous solutionproceeds at an excessively high speed, as a result, the patterning bythe change in the polarity cannot be obtained. The monomer unit contentis still more preferably from 30 to 50 mol %.

[0072] In the case where the alkali-soluble group is a phenolic hydroxylgroup, the monomer unit content is preferably from 20 to 99 mol %, morepreferably from 50 to 95 mol %. If the monomer unit content is less than30 mol %, the alkali solubility is insufficient and the patterningcannot be satisfactorily performed. The monomer unit content is stillmore preferably from 80 to 95 mol %.

[0073] In this negative resist composition, the content of the secondpolymer is not particularly limited, and it may be sufficient if in viewof the relationship with the first polymer, the content is large enoughto maintain the alkali solubility of the composition as a whole and atthe same time insolubilize the alkali-soluble group of the firstpolymer. In this negative resist composition, the second polymer contentis preferably from 0.1 to 80 wt % based on the total polymer weight ofthe first and second polymers.

[0074] Furthermore, in this negative resist composition of the presentinvention, the molecular weight of the second polymer is notparticularly limited and it may be sufficient if in view of therelationship with the first polymer, the alkali solubility of thecomposition as a whole can be maintained. In this negative resistcomposition, the molecular weight of the second polymer is preferablyfrom 500 to 100,000.

[0075] In the negative resist composition of the present invention, acompound having an alcohol structure may further be added. In the casewhere the alcohol structure of the second polymer is lacking, by furtheradding another compound having an alcohol structure, theinsolubilization of the exposed area of this negative resist in a basicaqueous solution can be accelerated without fail.

[0076] The above-described compound having an alcohol structurepreferably contains a tertiary alcohol structure. This compound reacts,similarly to the second polymer having an alcohol structure, with thealkali-soluble group of the first polymer, so that the insolubilizationof the alkali-soluble group of the first polymer in a basic aqueoussolution can be accelerated in the exposed area.

[0077] Examples of the alcohol structure which can be used include anallyl alcohol structure and a secondary or tertiary alcohol structure.Among these, a tertiary structure is preferred. The compound having thisstructure is particularly effective because it can reacts with thealkali-soluble group and greatly contributes to the formation of anegative pattern.

[0078] From the standpoint that the compound having an alcohol structuremust have a boiling point sufficiently high not to vaporize during theordinary resist processing and lose its function, the boiling point ofthe compound having an alcohol structure is preferably at least 130° C.or more.

[0079] In this negative resist, the compound having an alcohol structurepreferably contains an alicyclic structure or a polynuclear alicyclicstructure. By having such a structure, the etching resistance at theetching can also be improved.

[0080] In this negative resist composition, the compound having analcohol structure preferably contains at least one hydroxyl group,ketone group or alkyloxycarbonyl group.

[0081] Furthermore, in this negative resist composition, the firstpolymer may further contain an alkali-soluble group selected from alactone ring, an imide ring and an acid anhydride. When the firstpolymer contains this weak alkali-soluble group as the second monomerunit, the alkali solubility speed can be easily controlled.

[0082] In the negative resist composition of the present invention, themolecular weight of the first polymer is suitably from 2,000 to1,000,000.

[0083] In the negative resist composition of the present invention, thephotoacid generator (PAG) content depends on the strength of the acidgenerated after the composition is exposed to an exposure light source,however, usually, the content is suitably from 0.1 to 50 wt % (apercentage to the total polymer weight of the first and secondpolymers), preferably from 1 to 15 wt %. The molecular weight (weightaverage molecular weight) of the base resin is suitably from 2,000 to1,000,000, preferably from 5,000 to 100,000, more preferably from 3,000to 50,000. The molecular weight (weight average molecular weight) of thesecond polymer having on the side chain an alcohol structure capable ofreacting an alkali-soluble group is suitably from 300 to 1,000,000,preferably from 500 to 100,000, more preferably from 1,000 to 10,000.

[0084] The resist composition of the present invention is preferablyprovided in the form of a solution obtained by dissolving it in asolvent selected from the group consisting of ethyl lactate, methyl amylketone, methyl-3-methoxypropionate, ethyl-3-ethoxypropionate, propyleneglycol methyl ether acetate and a mixture thereof. The resistcomposition may further contain, if desired, a solvent selected from thegroup consisting of butyl acetate, γ-butyrolactone, propylene glycolmethyl ether and a mixture thereof, as an auxiliary solvent.

[0085] Another object of the present invention can be achieved by amethod for forming a resist pattern, comprising a series of steps forcoating the negative resist composition on a treated substrate, i.e.,target substrate as defined hereinafter, to form a resist film, forselectively exposing the resist film by a radiation for forming an imageto accelerate the decomposition of said photoacid generator, and fordeveloping the exposed resist film with a basic aqueous solution.

[0086] In the method for forming a resist pattern according to thepresent invention, the resist film formed on a treated substrate ispreferably subjected to a heat treatment before and after the step ofperforming the selective exposure thereof. More specifically, in thepresent invention, the resist film is preferably subjected to apre-baking treatment before the exposure thereof and at the same time toa post-baking treatment described above as PEB (post exposure baking)after the exposure but before the development. These heat treatments canbe advantageously performed by an ordinary method.

[0087] Although the resist composition of the present inventionpreferably has an absorbance of 1.75/μm or less at the wavelength of theexposure light source (from 150 to 300 nm) for obtaining satisfactorypatterning characteristics, in the case of using EB as the light source,the absorbance is not particularly limited.

[0088] Examples of the basic aqueous solution used as the developerinclude an aqueous solution of a metal hydroxide belonging to Group I orII, represented by potassium hydroxide, and an aqueous solution of anorganic base not containing a metal ion, such as tetraalkylammoniumhydroxide. Among these, preferred is an aqueous solution oftetramethylammonium hydroxide. In order to improve the developmenteffect, additives such as surfactant may also be added.

FOURTH INVENTION

[0089] The objects in the fourth aspect of the present invention areachieved by a negative resist composition wherein the molecular weightdistribution of the sections rendered insoluble by light exposure isbetween 1 and 2 inclusive, as an invention based on limitation of themolecular weight distribution.

[0090] According to the present invention, since the insolubilizedsections are formed primarily by a reaction based on polarity changes,it is possible to provide a resist composition with vastly improvedsensitivity and resolution without the problem of pattern swelling.

[0091] The molecular weight distribution is the value obtained bydividing the weight average molecular weight by the number averagemolecular weight. With conventional resists, the molecular weight variesconsiderably depending on crosslinking reaction and the variationdiffers widely for the particular molecule; the molecular weightdistribution of the insolubilized sections is therefore usually a valueof from 3 to 4 or higher, whereas that of the resist composition of theinvention is in the range of 1 to 2 inclusive, so that the polymer usedis more uniform. Since this type of resist does not undergo “gelling” bymolecular weight increase, it has an advantage in that the resist thathas transferred the required pattern can be easily released with anorganic solvent or the like.

[0092] The negative resist composition may also have the structuredescribed in the claim, containing a base resin which comprises analkali-soluble polymer, a photo acid generator which is capable ofdecomposing upon absorption of image-forming radiation to generate anacid, and an alicyclic alcohol with a reactive site that can undergodehydration bonding reaction with the alkali-soluble group of the baseresin in the presence of the acid generated by the photo acid generator.

[0093] According to the present invention, there is included analicyclic alcohol with a reactive site that can undergo dehydrationbonding reaction with the alkali-soluble group of the base resin, andtherefore the polarity change is increased when it is added to analkali-soluble polymer, while the etching resistance can also beimproved. Furthermore, since the molecular weight distribution at thesections insolubilized by light exposure is in the range of 1 to 2inclusive, it is possible to give a negative resist composition withhigher sensitivity and higher resolution.

[0094] The base resin in the negative resist composition preferably hasa molecular weight distribution of between 1 and 1.5 inclusive. Using abase resin with a molecular weight distribution in this range will allowthe molecular weight distribution of the sections insolubilized by lightexposure to be more reliably confined to the range of 1 to 2 inclusive.

[0095] Throughout this specification, a base resin with a molecularweight distribution of from 1 to 1.5 inclusive before light exposurewill sometimes be referred to as a “monodisperse resin”. Themonodisperse resin need only be uniform to fall within theabove-mentioned range, and the base resin may also have the constructionof a copolymer containing a number of different monomer units.

[0096] The negative resist composition of the present inventionpreferably has a base resin with a weight average molecular weight of atleast 2000 as described in claim 3, and more preferably the weightaverage molecular weight of the base resin is 3000 to 20,000. If theweight average molecular weight of the base resin is too low thesensitivity and resolution may be reduced, and if it is too high thelower solubility may result in a lower dissolution rate for thereaction, creating an undesirably low solubility. The most preferredrange for the weight average molecular weight is from 5000 to 10,000.Using a base resin with a weight average molecular weight in this rangecan give a negative resist composition with high solubility and highresolution. Here, the preferred molecular weight is specified by theweight average molecular weight because the base resin is composed of apolymer.

[0097] From the standpoint of controlling the molecular weight of eachmolecule of the polymer composing the base resin used according to thesecond aspect of the invention, the object described above is alsoachieved by a negative resist composition containing a base resin whichcomprises an alkali-soluble polymer, a photo acid generator which iscapable of decomposing upon absorption of image-forming radiation togenerate an acid, and an alicyclic alcohol with a reactive site that canundergo dehydration bonding reaction with the alkali-soluble group ofthe base resin in the presence of the acid generated by the photo acidgenerator, wherein no more than 10 wt % thereof consists of componentswith a molecular weight of under 2000 in said base resin.

[0098] The present inventors have confirmed that using a base resincontaining a low molecular weight portion with a molecular weight ofunder 2000 drastically reduces the sensitivity and resolution of theresist. This low molecular weight portion is believed to hamper thesolubility-suppressing effect in basic aqueous solutions. It was foundthat when the low molecular weight components of under 2000 are limitedto no more than 10 wt %, it is possible to obtain a favorable negativeresist composition in which the aforementioned undesirable effect isinhibited. The low molecular weight components of below 2000 morepreferably constitute no more than 3 wt % of the base resin. Here, themolecular weight is not the weight average molecular weight explainedabove, but rather the (actual) molecular weight of each polymer moleculecomposing the base resin.

[0099] By limiting the low molecular weight components with a molecularweight of below 2000 to no more than 10 wt % of the base resin it ispossible to give a resist composition with high sensitivity and highresolution, but a resist composition with even higher sensitivity andresolution can be obtained by giving the base resin a monodisperseproperty, as mentioned above.

[0100] The base resin of a negative resist composition according to thepresent invention preferably contains a phenol-based compound. Aphenol-based resin facilitates adjustment of the molecular weightdistribution and cutting of the low molecular weight portions.

[0101] The base resin is preferably polyvinylphenol or a copolymer ofvinylphenol with another monomer. Polyvinylphenol is preferred as thebase resin because it is readily obtainable and its monodispersion iseasy to accomplish.

[0102] The alicyclic alcohol of a negative resist composition accordingto the present invention preferably has an adamantane structure, asdescribed in claim 6. An alicyclic alcohol with an adamantane structurecan more readily promote insolubilization of the light exposed sections.

[0103] The alicyclic alcohol of a negative resist composition of thepresent invention preferably has a tertiary alcohol structure with astereochemically fixed structure. An alcohol with such a structure canmore readily promote insolubilization of the light exposed sections.

[0104] The tertiary alcohol of a negative resist composition of thisinvention is preferably a 1-adamantanol or a derivative thereof.

[0105] The photo acid generator of a negative resist compositionaccording to the present invention is preferably one selected from thegroup consisting of onium salts, halogenated organic substances andsulfonic acid esters.

[0106] The onium salt in the negative resist composition of thisinvention may be any one selected from the group consisting of thefollowing formulas (A) to (D).

[0107] where X=CF₃SO₃, CF₃CF₂CF₂CF₂SO₃, SbF₆, AsF₆, BF₄ and PF₆.

[0108] The halogenated organic substance in the negative resistcomposition of this invention may be a triazine with a halogen in thestructure or an isocyanurate with a halogen in the structure.

[0109] A high sensitivity, high resolution resist pattern may beobtained by a negative resist pattern forming method which comprises theseries of steps including coating a negative resist compositionaccording to the present invention onto a target substrate, selectivelyexposing the formed resist film to image-forming radiation that caninduce decomposition of the photo acid generator of the resistcomposition, and developing the exposed resist film with a basic aqueoussolution.

[0110] Furthermore, according to the present invention, there is alsoprovided a method for the production of electronic devices using thenegative resist composition of the present invention, i.e., first tofourth inventions described above.

[0111] The production process of electronic devices according to thepresent invention is characterized by using as a masking means a resistpattern formed from the negative resist composition of the presentinvention to selectively removing the underlying target substrate,thereby forming a predetermined functional element layer. The definitionof the term “functional element layer” will be described hereinafter.

[0112] The production process of electronic devices is preferablycarried out by the following steps:

[0113] coating the negative resist composition onto the targetsubstrate,

[0114] selectively exposing the formed resist film to image-formingradiation that can induce decomposition of the photo acid generator ofthe resist composition,

[0115] developing the exposed resist film with a basic aqueous solutionto form a resist pattern, and

[0116] etching the target substrate in the presence of the resistpattern as a masking means to form the functional element layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0117]FIGS. 1A to 1F illustrate, in sequence, the production process ofthe MOS transistor according to the present invention, and

[0118]FIGS. 2A to 2I illustrate, in sequence, the production process ofthe thinfilm magnetic recording head according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0119] The present invention will be further described with regard tothe negative resist composition of the present invention (each of thefirst to fourth inventions) as well as the method for the formation ofresist patterns and method for the production of electric devices usingthe resist composition of the present invention. Note, however, withregard to the resist composition, that the descriptions of thecomponents in the resist composition according to each invention will beomitted or simplified if they are neglectable, to avoid duplication ofthe descriptions.

FIRST INVENTION

[0120] The negative resist composition of the present invention (firstinvention) comprises, as an essential constituent element, afilm-forming polymer that is itself soluble in basic aqueous solutionsand includes a first monomer unit with an alkali-soluble group and asecond monomer unit with an alcohol structure that can react with thealkali-soluble group, which serves as the base resin. Here, the term“polymer” is used in a wide sense which will be explained in greaterdetail below, but it encompasses not only binary copolymers andterpolymers, but also simple polymers (homopolymers). In the case of ahomopolymer the first monomer unit and second monomer unit will be thesame, with the alkali-soluble group and the alcohol structure that canreact with the alkali-soluble group coexisting in one monomer unit. Thistype of film-forming polymer may have any structure so long as it canbasically retain suitable alkali solubility in the basic aqueoussolution used as the developer. Even poly copolymers such as terpolymersmay have any structure so long as they can retain suitable alkalisolubility.

[0121] The film-forming copolymer used as the base resin in a resistcomposition according to the invention may include a variety of moietiesas the polymer main chain, and preferred for the first and secondmonomer units are (meth)acrylic acid-based monomer units, itaconicacid-based monomer units, vinylphenol-based monomer units, vinylbenzoicacid-based monomer units, styrene-based monomer units,bicyclo[2.2.1]hept-5-ene-2-carboxylic acid-based monomer units,N-substituted maleimide-based monomer units and monomer units with anester group containing a multiple or polycyclic alicyclic hydrocarbonportion. These monomer units are useful from the standpoint of givingdry etching resistance comparable to that of novolac resists. The firstand second monomer units may also be the same or different. Also, whenthe first and second monomer units are the same as explained above, themonomer unit may be any of those mentioned above.

[0122] Of the monomer units mentioned above, (meth)acrylate-basedmonomer units are particularly important from the standpoint of lowabsorption of light with a wavelength in the deep ultraviolet region,when deep ultraviolet rays are used as the exposure light source. Inother words, when deep ultraviolet rays are used as the exposure lightsource, it is generally preferred to use a copolymer with a structurecontaining no aromatic rings that absorb significant light in the deepultraviolet region or chromophoric groups with a large molar absorptioncoefficient, such as conjugated double bonds.

[0123] The first monomer unit of the film-forming polymer must have analkali-soluble group in its structure. The alkali-soluble groups thatmay be introduced here include the various groups that are commonlyintroduced into base resin polymers in the field of chemicalamplification resists, but the preferred ones are usually carboxylicacid groups, sulfonic acid groups, amido groups, imido groups, phenolgroups, acid anhydride groups, thiol groups, lactonic acid ester groups,azalactone groups, hydroxyamide groups, oxazone groups, pyrrolidonegroups and hydroxyoxime groups, with carboxylic acid groups, sulfonicacid groups, amido groups, imido groups and hydroxyamide groups beingpreferred.

[0124] In the film-forming polymer of the invention, the proportion ofthe first monomer unit in the polymer is not particularly restricted solong as the polymer itself exhibits appropriate alkali solubility, butin order to achieve a suitable alkali dissolution rate (ADR) (measuredwith a 2.38% tetramethylammonium hydroxide aqueous solution, 100-10,000Å/sec) considered to be practical for the negative resist intended forthe invention, for example, when the copolymer contains a carboxylicacid as the alkali-soluble group in a copolymer of two or morecomponents, the proportion is preferably in the range of 10-90 molepercent, and even more preferably in the range of 30-70 mole percent. Ifthe content of the first monomer unit is under 10 mole percent, thealkali solubility becomes insufficient, making it impossible toaccomplish satisfactory patterning. Conversely, if the content of thefirst monomer unit is above 90 mole percent the alkali solubilitybecomes too strong, resulting in an excessively high dissolution rate inbasic aqueous solutions and making it impossible to accomplishpatterning that depends on polarity changes. The content of the firstmonomer unit is even more preferably in the range of 30-50 mole percent.

[0125] When the first monomer unit of the film-forming polymer containsa phenolic hydroxyl group as the alkali-soluble group, the content ofthat monomer group is preferably in the range of 30-99 mole percent, andmore preferably in the range of 50-95 mole percent. If the content ofthe first monomer unit is under 30 mole percent the alkali solubilitybecomes insufficient, making it impossible to accomplish satisfactorypatterning. Likewise, it becomes impossible to accomplish satisfactorypatterning if the content of the first monomer unit is above 99 molepercent. The preferred content for the first monomer unit is in therange of 80-95 mole percent.

[0126] The second monomer unit of the film-forming polymer must have onits side chain an alcohol structure capable of reacting with thealkali-soluble group of the first monomer unit. The alcohol structure tobe introduced here may be widely modified depending on the desiredeffect, but according to the experience of the present inventors atertiary alcohol structure is particularly useful. A tertiary alcoholstructure more readily undergoes dehydration reaction than a secondaryalcohol structure.

[0127] Suitable tertiary alcohol structures for carrying out theinvention include those represented by any of the following formulas (I)to (IV).

[0128] Preferred tertiary alcohol structure (I):

[0129] where R is linked to the main chain of the monomer unit andrepresents any bonding group that is copolymerizable with the firstmonomer. This bonding group R is therefore copolymerizable with themonomer unit with the alkali-soluble group, and its structure is notparticularly specified so long as it does not adversely influence theeffect intended by the invention. Examples of suitable bonding groupsfor R include linear or branched hydrocarbon groups of 1-6 carbons suchas methyl or ethyl, and the group —O—.

[0130] R₁ and R₂ are the same or different and each represents a linear,branched or cyclic hydrocarbon group, for example, an alkyl group of 1-8carbons such as methyl or ethyl, or an alicyclic or aromatic hydrocarbongroup such as phenyl; otherwise, as explained below, the twosubstituents R₁ and R₂ may be bonded together to form a cyclic system,such as an alicyclic or aromatic hydrocarbon group or heterocyclicgroup.

[0131] Preferred tertiary alcohol structure (II):

[0132] where R is the same as defined above.

[0133] R_(x) represents a hydrocarbon group of 1-8 carbons, for example,a linear or branched or cyclic hydrocarbon group such as methyl, ethylor phenyl, and p is an integer of 2-9.

[0134] Preferred tertiary alcohol structure (III):

[0135] where is the same as defined above.

[0136] Y represents a hydrogen atom or an optional substituent selectedfrom the group consisting of alkyl, alkoxycarbonyl, ketone, hydroxyl andcyano groups. The bonding site of substituent Y with respect to thefollowing alicyclic hydrocarbon group is not particularly restricted.

[0137] Z represents a plurality of atoms necessary to complete thealicyclic hydrocarbon group. The alicyclic hydrocarbon group may be anyof a variety of groups, but preferably has on of the following compoundsas the skeleton.

[0138] Adamantane and its derivatives,

[0139] Norbornane and its derivatives,

[0140] Perhydroanthracene and its derivatives,

[0141] Perhydronaphthalene and its derivatives,

[0142] Tricyclo[5.2.1.0^(2.6)]decane and its derivatives,

[0143] Bicyclohexane and its derivatives,

[0144] Spiro[4,4]nonane and its derivatives,

[0145] Spiro[4,5]decane and its derivatives, and the like. Particularlypreferred among these alicyclic hydrocarbon groups are those withadamantane and its derivatives as skeletons, an example of which is thecompound represented by the following formula (III-1):

[0146] where R and Y are both the same as defined above.

[0147] Preferred tertiary alcohol structure (IV):

[0148] where R and Y are both the same as defined above.

[0149] BA represents a plurality of atoms necessary to complete thebicycloalkane ring. The bicycloalkane ring may be any of a variety ofgroups, but is preferably bicyclohexane, bicyclooctane, bicyclodecane orthe like, and more preferably bicyclooctane. Bicyclooctane may berepresented by the following formula (IV-1):

[0150] where R and Y are both the same as defined above.

[0151] The proportion of the second monomer unit in the film-formingpolymer of the invention may be widely varied depending on theproperties desired for the resist composition, but its preferred rangewill usually be 0.1-70 mole percent based on the total amount of thefilm-forming polymer.

[0152] The film-forming polymer used as the base resin according to theinvention contains the aforementioned first and second monomer units.According to a preferred mode of the invention, the first or secondmonomer unit, or both monomer units may further contain, in addition tothe alkali-soluble group to be included in the first monomer unit, aweaker alkali-soluble group. The additional alkali-soluble group willnormally be bonded to the side chain of the monomer unit. Suitablealkali-soluble groups include, but are not limited to, for example,lactone rings, imide rings and acid anhydrides. In some cases, theadditional alkali-soluble group in the film-forming polymer of theinvention may be included in a third, fourth or more monomer units usedin addition to the first and second monomer units.

[0153] The above explanation is a summary of the film-forming polymerused as the base resin in the negative resist composition of theinvention. The invention will become more clearly understood by thefollowing explanation of the chemical amplification mechanism in theresist composition of the invention, with reference to a specificfilm-forming polymer.

[0154] The film-forming polymer referred to here is a binary copolymercomprising a first monomer unit containing a phenol group as thealkali-soluble group on the side chain, and a second monomer unitcontaining an adamantyl group similar to formula (III-1) above as thetertiary alcohol structure on the side chain, as illustrated by thereaction formula shown below. In the formulas, Y is the same as definedabove and X is an optional substituent, for example, a hydrogen atom, ahalogen atom (such as chlorine or bromine), a lower alkyl group (such asmethyl or ethyl), etc. The letters m and n are the numbers of monomerunits (repeating units) necessary to give the prescribed molecularweight desired for the copolymer.

[0155] When the resist composition comprising both the film-formingpolymer and the photo acid generator (PAG) is coated onto a targetsubstrate and the resist film is prebaked and then exposed toimage-forming radiation, the PAG in the resist composition absorbs theradiation and decomposes to generate an acid. Subsequent post exposurebaking (PEB) allows the generated acid to act as a catalyst to produce areaction illustrated below at the exposed sections of the film. That is,a dehydration reaction occurs at the tertiary alcohol structure of thesecond monomer unit of the film-forming polymer, and the tertiaryalcohol structure produced by the reaction then reacts with the nearbyphenol ring. Numerous such reactions proceed simultaneously, as shown,result in products of reaction between the phenol rings and the tertiaryalcohol structures, and products of protection of the phenol rings withthe tertiary alcohol structures, thus altering the alkali solubility ofthe polymer.

[0156] In this reaction, the cation resulting from the dehydrationreaction initiates an electrophilic substitution reaction with thehydroxyl group of the vinylphenol ring or the ortho carbon of the ring.In the former case, the cation reacts directly with the alkali solublegroup to reduce the alkali solubility, while in the latter case thestrong hydrophobicity and steric hindrance of the adamantyl group lowersthe alkali solubility. Thus, the alkali solubility is considerablylowered at the light exposed sections, giving a negative pattern.

[0157] The next illustration, as shown by the reaction formula below, isa case where the base resin used is a binary copolymer comprising afirst monomer unit containing a carboxyl group as the alkali-solublegroup on the side chain, and a second monomer unit containing the sameadamantyl group as above as the tertiary alcohol structure on the sidechain. Here, Y, X, m and n are all the same as defined above. In thiscase of a binary copolymer-containing resist composition as well,irradiation with image-forming radiation results in dehydration reactionwith the alcohol and reaction of the tertiary alcohol structure with itsneighboring carboxyl group. As a result of this reaction, the alkalisolubility of the polymer is reduced. The alkali solubility is thereforeconsiderably lowered at the light exposed sections, giving a negativepattern.

[0158] The resist composition of the invention is an “amplificationcomposition” that includes an alcohol structure in the film-formingpolymer used as the base resin, whose reaction can regenerate a protonacid; a high resolution can thereby be achieved. Furthermore, since theresist composition loses its alkali soluble group after the sensitivegroup is protected (specifically, it is converted to an ether or ester),the exposed sections of the resist film become alkali-insoluble, thusallowing formation of a negative pattern after development with a basicaqueous solution. Moreover, since the present invention accomplishespattern formation using a polarity change produced in the polymer, thepattern formation can be accomplished without swelling.

[0159] If the polymer in the film-forming polymer used as the base resinin the resist composition of the invention is in the form of aterpolymer, it preferably has a relative strong alkali-soluble grouprepresented by carboxylic acid or phenol introduced into the firstmonomer unit, and a weaker alkali-soluble group such as a lactonestructure, an acid anhydride such as succinic anhydride or glutaricanhydride, an imide ring structure, etc. introduced into the secondmonomer unit. In such cases, the contents of the strong alkali-solublegroup and weak alkali-soluble group may be controlled to allow easyadjustment of the alkali dissolution rate of the base resin to thepreferred value. The third monomer unit preferably has a functionalgroup with etching resistance. Thus, by appropriately selecting thesubstituents introduced into each of the monomer units and effectivelytaking advantage of the respective functional group functions, it ispossible to achieve a higher performance resist.

[0160] The alcohol structure in the film-forming polymer of the resistcomposition is preferably a tertiary alcohol structure. This is becausethe presence of a tertiary alcohol structure more readily allowsdehydration reaction. According to the present invention, a compoundwith an alcohol structure that makes such a reaction possible (referredto as “alcohol structure-containing compound” throughout the presentspecification) is included in the resist composition as an additive,together with introduction of the aforementioned alcohol structure intoa monomer unit of the polymer. The structure of this added alcoholstructure-containing compound is not particularly restricted, butconsidering that its main purpose is to contribute to improved etchingresistance, it is preferably a polycyclic alicyclic compound or acompound with a benzene ring in the molecule. Furthermore, the compoundpreferably has a tertiary alcohol structure that more readily undergoesdehydration reaction with an acid.

[0161] Returning to the explanation of the film-forming polymer, apreferred structure of a polymer suitable for carrying out the inventionwill now be discussed.

[0162] The film-forming polymer used as the base resin in the resistcomposition of the invention is not particularly restricted so long asthe above-mentioned conditions, especially the condition of a suitablealkali dissolution rate, are satisfied. In consideration of giving dryetching resistance comparable to that of novolac resists, usefulfilm-forming polymers include, but are not limited to, the following:(meth)acrylate-based polymers, vinylphenol-based polymers, vinylbenzoicacid-based polymers, N-substituted maleimide-based polymers,styrene-based polymers, bicyclo[2.2.1]hept-5-ene-2-carboxylic acid-basedpolymers, etc., that have with polycyclic alicyclic hydrocarboncompounds in ester groups.

[0163] Of the film-forming polymers mentioned above,(meth)acrylate-based polymers, i.e. acrylate-based or methacrylate-basedpolymers, are important from the standpoint of low absorption of lightwith a wavelength in the deep ultraviolet region, when a deepultraviolet ray source and especially a light source with a wavelengthof 220 nm or smaller is used as the exposure light source. In otherwords, when deep ultraviolet rays are used as the exposure light source,it is generally preferred to use a copolymer with a structure containingno aromatic rings that absorb significant light in the deep ultravioletregion or chromophoric groups with a large molar absorption coefficient,such as conjugated double bonds.

[0164] Since the use of an extremely short wavelength exposure lightsource such as an ArF excimer laser as the light source requirestransparency at that wavelength (193 nm) along with dry etchingresistance, it is recommended to use as the film-forming polymer apolymer with a polycyclic alicyclic hydrocarbon structure-containingester group with high dry etching resistance such as mentioned above,typical examples of which are adamantyl, bicyclo[2.2.2]octane andnorbornyl groups.

[0165] The molecular weight (weight average molecular weight, Mw) of thefilm-forming polymer described above may be varied within a wide rangedepending on the structure of the polymer, but it is normally preferredto be in the range of 2,000-1,000,000, and more preferably in the rangeof 3,000-50,000.

[0166] The monomer unit (second monomer unit) with an alcohol structureto be included in the film-forming polymer described above encompasses,but is not limited to, for example, the following vinyl monomers withalcohol structures as the ester groups or ether groups.

[0167] In these formulas, Y and R_(x) are the same as defined above, andR₆-R₈ may be the same or different and each represents a hydrogen atomor an optional substituent, for example, a halogen atom such as chlorineor bromine, a cyano group or a linear, branched or cyclic alkyl group of1-4 carbons such as methyl, ethyl or methylol, the substituent beingfurther substituted when necessary, and p and q each represent aninteger or 1-6.

[0168] Film-forming compositions that may be advantageously used forcarrying out the invention include, but are not limited to, thefollowing preferred polymers. In the general formulas that follow, X, Yand R_(x) are the same as defined above, ALC represents the alcoholstructure described above, and 1, m and n are the respective numbers ofmonomer units (repeating units) necessary to obtain the aforementionedweight average molecular weight.

[0169] In addition to the aforementioned typical film-forming polymersfor carrying out the invention, there may also be advantageously usedhalf-esters of maleic acid or fumaric acid, and monoesters of itaconicacid.

[0170] The film-forming polymer to be used as the base resin for theinvention may be prepared using a polymerization process commonlyutilized in the field of polymer chemistry. For example, a(meth)acrylate-based copolymer can be successfully prepared by freeradical polymerization of the prescribed monomers required for itspreparation, by way of heating in the presence of a free radicalinitiator. As examples of free radical initiators there may be mentioned2,2′-azobisisobutyronitrile (AIBN) and dimethyl-2,2-azoisobisbutyrate(MAIB). Film-forming polymers other than (meth)acrylate-based polymersmay also be successfully prepared by similar commonly employedpolymerization processes.

[0171] As alluded to above, the resist composition of the inventionpreferably also contains a compound with an alcohol structure in themolecule, in addition to the aforementioned film-forming polymer. Thealcohol structure of the alcohol structure-containing compound which isalso added may be either a secondary alcohol structure or tertiaryalcohol structure, but a tertiary alcohol structure is moreadvantageous. The tertiary alcohol structure may be the same as thepreviously mentioned one, or depending on the case it may be a differentone. The alcohol structure-containing compound also preferably has aboiling point of at least 130° C. If the boiling point of the alcoholstructure-containing compound is below 130° C., the heating of theprebaking step carried out prior to light exposure may cause escape ofthe compound itself, thus making it impossible to achieve the expectedeffect.

[0172] The alcohol structure-containing compound preferably includes analicyclic structure or polycyclic alicyclic structure. The compoundpreferably also includes a substituent which is the same as thesubstituent Y included in the alcohol structure of the second monomerunit of the film-forming polymer, for example, a hydroxyl group, ketonegroup or alkoxycarbonyl group. Examples of alcohol structure-containingcompounds that are useful for carrying out the invention include, butare not limited to, the compounds represented by the following generalformulas. In these general formulas, Y and R_(x) are the same as definedabove, and p is an integer of 1-6.

[0173] The proportion of the aforementioned alcohol structure-containingcompound in the resist composition of the invention will depend on theamount of the alkali-soluble group included in the film-forming polymer,or in other words on the alkali dissolution rate of the polymer, but fora polymer with a suitable alkali dissolution rate such as describedabove, the amount of addition is preferably in the range of 1-100 wt %,and more preferably in the range of 10-50 wt %, based on the totalamount of the polymer.

[0174] The manner of using the alcohol structure-containing compoundwill now be further explained. Of the film-forming polymers that areuseful for carrying out the invention, (meth)acrylate-based copolymersare well known to have high transparency in the deep ultraviolet range,and appropriate selection of this polymer structure and a structurecontaining no chromophoric groups with a large molar absorptioncoefficient near the exposure wavelength range for the structure of thealcohol structure-containing compound used therewith, in combinationwith a suitable amount of a photo acid generator, can give a highlysensitive resist that is advantageously suited for light exposure usingdeep ultraviolet rays.

[0175] The photo acid generator (PAG) used in combination with theaforementioned film-forming polymer in the chemical amplification resistof the invention may be a photo acid generator that is commonly used inthe field of resist chemistry, i.e., a substance the produces a protonacid upon irradiation with radiation such as ultraviolet rays, farultraviolet rays, vacuum ultraviolet rays, an electron beam, X-rays,laser light or the like. Suitable photo acid generators that may be usedfor the invention include, but are not limited to, those represented bythe following formulas. (1) Onium salts, for example:

(R¹)₂—I⁺X⁻ ₁

(R¹)₃—S⁺X⁻ ₁

[0176] where each R¹ may be the same or different and represents, forexample, a substituted or unsubstituted aromatic group, such as a phenylgroup substituted with phenyl, a halogen, methyl, t-butyl, an aryl groupor the like, or an alicyclic group, and

[0177] X₁ represents, for example, BF₄, BF₆, PF6, AsF₆, SbF₆, CF₃SO₃,ClO₄, etc.

[0178] In spite of simple structure thereof, onium salts haveparticularly notable effects of inducing a condensation reaction, andthus they are preferably used as the photo acid generator. Typicalexamples of useful onium salts include:

[0179] wherein X₁ is as defined above.

[0180] (2) Sulfonic acid esters, for example:

[0181] (3) Halogenated compounds, for example:

[0182] where X₂ represents a halogen atom such as Cl, Br or I, eachbeing the same or different, and one of the —C(X₂)₃ groups in theformula may be a substituted or unsubstituted aryl group or alkenylgroup.

[0183] Particularly, triazines or isocyanates containing halogen atom(s)in a molecule thereof may be advantageously used as the photo acidgenerator in the scope of the halogenated compounds. Typical examples ofsuch halogenated compounds include:

[0184] In addition to these photo acid generators, there may be alsoused, if necessary, the photo acid generators disclosed in JapaneseUnexamined Patent Publication (Kokai) No. 9-90637 and No. 9-73173, forexample.

[0185] The photo acid generators mentioned above can be used in theresist composition of the invention in various amounts suited for thedesired effect. The present inventors have found that the photo acidgenerator is preferably used in a range of 0.1 to 50 wt % based on thetotal amount of the film-forming polymer used as the base resin. Whenthe amount of the photo acid generator is over 50 wt %, excessive lightabsorption will prevent successful patterning. The amount of the photoacid generator used is even more preferably in the range of 1 to 15 wt %based on the total amount of the polymer.

[0186] The resist composition of the invention preferably has a specifictransmittance at the exposure light wavelength; that is, when the resistcomposition is used to form a resist film with a thickness of 1 μm byapplication onto a quartz substrate, it preferably has an absorbance ofno greater than 1.75 μm⁻¹ at the wavelength of the deep ultravioletexposure light source (180 to 300 nm), and therefore the structure ofthe film-forming polymer and photo acid generator and the amount of thephoto acid generator used should be considered in light of achievingsuch transmittance. Naturally, when an electron beam is used as theexposure light source it is possible to avoid the problem oftransmittance transparency, so that there is no particular need toconsider the amount of photo acid generator that is used.

[0187] The resist composition of the invention can usually beadvantageously used in the form of a resist solution, by dissolving theaforementioned film-forming polymer and photo acid generator, and,ifnecessary the alcohol structure-containing compound and other optionaladditives, in an appropriate organic solvent. Organic solvents that areuseful for preparation of resist solutions include, for example, ethyllactate, methyl amyl ketone, methyl-3-methoxypropionate,ethyl-3-ethoxypropionate, propyleneglycol methyl ether acetate, etc.,but there is no limitation to these solvents. The solvents may be usedalone, or if necessary two or more solvents may be used in admixture.The amount of these solvents to be used is not particularly restricted,but they are preferably used in an amount sufficient to achieve anappropriate viscosity for coating by spin coating or the like, as wellas for the desired resist film thickness.

[0188] Co-solvents may also be used with the aforementioned solvent(referred to as “primary solvent” throughout the present specificationfor distinction from additionally used solvents) if necessary in theresist solution of the invention. The use of a co-solvent is notnecessary when the solubility of the solutes is satisfactory or when thesolution can be evenly coated, but in cases where solutes with lowsolubility are used or the solution cannot be evenly coated as desired,it will usually be added in an amount of preferably 1-30 wt % and morepreferably 10-20 wt %, with respect to the primary solvent. Examples ofuseful co-solvents include, but are not limited to, butyl acetate,γ-butyrolactone and propyleneglycol methyl ether. These co-solvents,like the aforementioned primary solvent, may also be used alone or inmixtures.

SECOND INVENTION

[0189] The chemical amplification resist composition of the presentinvention (second invention) has a combination of:

[0190] (1) a base resin composed of an alkali-soluble polymer,

[0191] (2) a photoacid generator capable of decomposing upon absorptionof image-forming radiation to generate an acid, and

[0192] (3) an alicyclic alcohol with a reactive site that can undergodehydration reaction with the polymer of the base resin in the presenceof the acid generated by the photoacid generator, as components thatdirectly participate in the reaction for formation of the resistpattern.

[0193] Each of the reaction components will be explained in detailbelow, but first the acid-catalyzed reaction in the resist compositionof the invention will be explained to more clearly elucidate the conceptof the invention.

[0194] The alicyclic alcohol has a highly polar group such as analcoholic hydroxyl group in the molecule. In the presence of an acidcatalyst, such a substance reacts with the polar group of the base resin(a phenolic hydroxyl group or the like) to produce an ester or ether.Assuming the use of polyvinylphenol as the base resin and addition of a1-adamantanol as the alicyclic alcohol, primarily the following reactionoccurs by the action of the acid catalyst.

[0195] This one reaction results in a polarity change due toetherification of both the phenolic hydroxyl group of the base resin andthe alcoholic hydroxyl group of the alicyclic alcohol, such that bothare rendered alkali-insoluble. That is, by way of this reaction theobject of the invention which is “high polarity of the resin andadditives prior to light exposure, and low polarity of the resin andadditives after light exposure” is achieved.

[0196] The pathway of the acid-catalyzed reaction in the resistcomposition of the invention is not limited to the one pathway shownabove, and other reactions may also accompany it. As examples there maybe mentioned a reaction in which an adamantanol is added to the carbonatom at the position adjacent to the phenolic hydroxyl group of the baseresin, and a reaction in which the adamantanol groups are condensedtogether. These accompanying reactions can also contribute to thepolarity reduction due to ether conversion of the hydroxyl groups andsteric hindrance by the bulky alicyclic groups adjacent to the hydroxylgroups.

[0197] The alicyclic alcohol used as the third reaction component in theresist composition of the invention has a reaction site that can undergoa dehydration bond reaction with the base resin (alkali-soluble polymer)as the first reaction component, in the presence of the acid generatedby the photoacid generator as the second reaction component. The meritsof using the alicyclic alcohol according to the invention include thefollowing, which will be clarified by the explanation given below.

[0198] (1) The bulky structure results in a greater polarity change uponaddition to the alkali-soluble polymer;

[0199] (2) When used as a resist, it is possible to achieve high etchingresistance.

[0200] For carrying out the invention, the alicyclic alcohol may have asingle alcoholic hydroxyl group as the reaction site, or else it mayhave two or more alcoholic hydroxyl groups. Including a plurality ofalcoholic hydroxyl groups in the molecule can provide an effect based oncrosslinking in addition to the effect based on altered polarity.

[0201] It is preferred for an optional bonding group to lie between thealicyclic skeleton and the alcoholic hydroxyl group bonded to thealicyclic skeleton in the alicyclic alcohol that is used. As suitablebonding groups there may be mentioned groups of 1-6 atoms such aslinear, branched or cyclic hydrocarbon groups, which include alkyl, forexample. Such alcohols therefore encompass primary alcohols, secondaryalcohols and stereochemically unfixed alcohols.

[0202] Alicyclic alcohols with a variety of different structures may beused alone or in combinations. Basically speaking, the alicyclic alcoholused when carrying out the invention is preferably one with a bulkystructure. Specifically, useful alicyclic alcohols include monocyclicalcohol compounds of 4 or more carbons, for example, alcohol compoundswith a cyclohexane structure in the molecule, polycyclic alcoholcompounds of 6 or more carbons including bicyclic alcohol compounds with6 or more carbons, for example, alcohol compounds with a norbornanestructure or bicyclo[2.2.2]octane structure in the molecule, andtricyclic alcohol compounds of 8 or more carbon atoms, for example,alcohol compounds with a perhydroanthracene structure orperhydrophenanthrene structure in the molecule. Especially preferredalicyclic alcohols for carrying out the invention are alcohols with anadamantane structure in the molecule, with 1-adamantanols and theirderivatives being preferred. 1-adamantanols and their derivatives areuseful in that they can be easily obtained commercially.

[0203] The alicyclic alcohol also preferably has a boiling point of atleast 130° C. If the boiling point of the alcohol is below 130° C. theheating of the prebaking step carried out prior to light exposure maycause escape of the compound itself, thus making it impossible toachieve the expected effect. Stated differently, it is recommended forthe heating temperature for the prebaking step prearranged for thedesired effect to be considered beforehand, in order to allow selectionof an alicyclic alcohol with a boiling point above that temperature.

[0204] The following general formulas are typical instances of alicyclicalcohols that may be advantageously used for carrying out the invention.

[0205] In addition to these alicyclic alcohols, results of research bythe present inventors have demonstrated that alicyclic alcohols thatprovide the most desirable and greatest effect when carrying out theinvention are tertiary alcohols with a stereochemically fixed structure.This is attributed to the fact that reaction between the phenolichydroxyl group and tertiary alcohol of the base resin makes it difficultfor the resulting ether bond to be decomposed again after bonding, thusreturning to the phenolic hydroxyl group as shown below.

[0206] Here, for the ether bond to be decomposed again to become aphenolic hydroxyl group, it is believed necessary for the alkyl portionto shift from the pyramid conformation to the planar conformation.Primary alcohols, secondary alcohols and even tertiary alcohols whichhave a non-stereochemically fixed structure as does tert-butyl, canrotate freely in the planar conformation. It is believed thatregeneration of the phenolic hydroxyl groups by decomposition thereforeoccurs competitively, preventing the reaction from occurring asexpected.

[0207] In contrast, 1-adamantanols and their derivatives that are usedfor the invention have a structure that cannot readily adopt a planarconformation, and therefore it is believed that such regeneration of thephenolic hydroxyl groups by extraction occurs very rarely (see followingstructure formulas).

[0208] According to the invention, the aforementioned substituent willbe referred to as a “stereochemically fixed” substituent or simply a“rigid substituent”.

[0209] A few examples of 1-adamantanols that can be advantageously usedfor the invention include the following. 1-adamantanol derivatives thatmay likewise be used also include, but are not limited to, the compoundsshown below.

[0210] Other alicyclic alcohols that may be advantageously used for theinvention include the following.

[0211] None of these alicyclic alcohols can easily adopt a planarconformation, or in other words, they are stereochemically fixedtertiary alcohols.

[0212] The alicyclic alcohol in the resist composition of the inventionmay be used in various amounts required for the desired effect. Theamount of alicyclic alcohol used is usually preferred to be in the rangeof 2 to 60 wt %, and even more preferably in the range of 15 to 40 wt %,based on the total amount of the alkali-soluble polymer used as the baseresin. If the amount of the alicyclic alcohol is under 2 wt %, thereaction may still occur but the polarity change will be lower, makingit impossible to achieve the essential contrast as a negative resist.Conversely, if the amount of the alicyclic alcohol is above 60 wt %, agreater exposure dose will simply be necessary to complete thesubstituent reaction, creating a poorly cost-effective situation. Inaddition, when the alicyclic alcohol is added in such a large amount,the thermal properties of the resist as a whole may be inferior andother undesirable problems such as precipitation during resist coatingmay occur.

[0213] A base resin, i.e. an alkali-soluble polymer, is used as thefirst reaction component in the resist composition of the invention.Here, “polymer” is used in the wide sense, to include not onlyhomopolymers formed from a single type of monomer, but also copolymersincluding binary copolymers and terpolymers. When necessary, a polymerthat does not react with the alicyclic alcohol may also be used as anadditional base resin.

[0214] Polymers that may be used for carrying out the inventionbasically have any structure that can maintain appropriatealkali-solubility in basic aqueous solutions used as developers, whilecontributing to the dehydration reaction with the alicyclic alcohol. Inparticular, from the standpoint of achieving dry etching resistancecomparable to that of a novolac resist, useful alkali-soluble polymersinclude, but are not limited to, the following: (meth)acrylate-basedpolymers, phenol-based polymers (including vinylphenol-based polymers,vinylbenzoic acid-based polymers, etc.), N-substituted maleimide-basedpolymers, styrene-based polymers andbicyclo[2.2.1]hept-5-ene-2-carboxylic acid-based polymers. Thesepolymers may be used alone or in combinations of two or more types ofpolymers. (Meth)acrylate-based polymers and phenol-based polymers arerecommended for use according to the invention because they are easilyobtainable.

[0215] Such alkali-soluble polymers must have an alkali-soluble group inthe structure in order to maintain alkali-solubility. Alkali-solublegroups that may be introduced here include those that are commonlyintroduced into polymers as base resins in the field of chemicalamplification resists, but usually phenolic hydroxyl groups, carboxylicacid groups, sulfonic acid groups, amido groups, imido groups, acidanhydride groups, thiol groups, lactonic acid ester groups, azalactonegroups, hydroxyamide groups, oxazone groups, pyrrolidone groups andhydroxyoxime groups are preferred, with phenolic hydroxyl groups,carboxyl acid groups, sulfonic acid groups, amido groups, hydroxyamidegroups, and imido groups being especially preferred.

[0216] The alkali dissolution rate (ADR) derived from the alkali-solublegroup in the polymer is not particularly restricted so long as thepolymer itself exhibits suitable alkali solubility, but as measured witha 2.38% tetramethylammonium hydroxide aqueous solution, a range of 100to 10,000 Å/sec is considered to be practical for the negative resistintended for the invention. For example, when the copolymer contains acarboxylic acid as the alkali-soluble group in a copolymer of two ormore components, the proportion of the monomer unit with the carboxylicacid is usually preferably in the range of 10-90 mole percent, and evenmore preferably in the range of 30-70 mole percent. If the content ofthis monomer unit is under 10 mole percent, the alkali solubilitybecomes insufficient, making it impossible to accomplish satisfactorypatterning. Conversely, if the content of the monomer unit is above 90mole percent the alkali solubility becomes too strong, resulting in anexcessively high dissolution rate into basic aqueous solutions andmaking it impossible to accomplish patterning that depends on polaritychanges.

[0217] When one monomer unit of the alkali-soluble polymer contains aphenolic hydroxyl group as the alkali-soluble group, the content of thatmonomer group is preferably in the range of 30 to 99 mole percent, andmore preferably in the range of 50 to 95 mole percent. If the content ofthis monomer unit is under 30 mole percent the alkali solubility becomesinsufficient, making it impossible to accomplish satisfactorypatterning. Likewise, it becomes impossible to accomplish satisfactorypatterning if the content of the monomer unit is above 99 mole percent.

[0218] When the alkali-soluble polymer is in the form of a terpolymer,it is preferred to introduce a relative strong alkali-soluble group suchas a carboxylic acid or phenol into the first monomer unit, and tointroduce into the second monomer unit a weaker alkali-soluble groupwith, for example, a lactone structure, an acid anhydride such assuccinic anhydride or glutaric anhydride, or an imide ring structure. Inthis case, the contents of the strong alkali-soluble group and weakalkali-soluble group in each monomer unit may be controlled to alloweasy adjustment of the alkali dissolution rate of the base resin to thepreferred value. The third monomer unit preferably has a functionalgroup with etching resistance. Thus, by appropriately selecting thesubstituents introduced into each of the monomer units and effectivelytaking advantage of the respective functional group functions, it ispossible to achieve a higher performance resist.

[0219] Among the aforementioned alkali-soluble groups,(meth)acrylate-based polymers, i.e. acrylate-based or methacrylate-basedpolymers (polyacrylates, polymethacrylates, copolymers of acryl andother monomers, etc.) are important from the standpoint of lowabsorption of light with a wavelength in the deep ultraviolet region,when a deep ultraviolet ray source and especially a light source with awavelength of 220 nm or smaller is used as the exposure light source. Inother words, when deep ultraviolet rays are used as the exposure lightsource, it is generally preferred to use a copolymer with a structurecontaining no aromatic rings that absorb significant light in the deepultraviolet region or chromophoric groups with a large molar absorptioncoefficient, such as conjugated double bonds.

[0220] Since the use of an extremely short wavelength exposure lightsource such as an ArF excimer laser as the light source requirestransparency at that wavelength (193 nm) along with dry etchingresistance, it is recommended to use a (meth)acrylate-based polymer witha polycyclic alicyclic hydrocarbon structure-containing ester group withhigh dry etching resistance, typical examples of which are adamantyl,bicyclo[2.2.2]octane and norbornyl groups.

[0221] As concerns the combined use of an alicyclic alcohol as the thirdreaction component, (meth)acrylate-based polymers are well known to havehigh transparency in the deep ultraviolet range, and appropriateselection of a structure having no chromophoric groups with a largemolar absorption coefficient near the exposure wavelength for thestructure of this polymer as well as the structure of the alicyclicalcohol used therewith, in combination with a suitable amount of aphotoacid generator (the second reaction component), can provide a highsensitivity resist composition that can also be advantageously appliedfor deep ultraviolet ray exposure.

[0222] As phenol-based polymers, particular advantages may be affordedby using polyvinylphenol, phenol-novolac copolymers, cresol-novolaccopolymers and the like. Copolymers of a monomer with a phenolichydroxyl group and another monomer may also be used. For adjustment ofthe solubility, there may be used a resin in which a portion of thephenolic hydroxyl groups have been etherified.

[0223] The desired polarity change can also be achieved using a polymerwith carboxyl groups as the base resin instead of a phenol-basedpolymer, since it can produce an esterification reaction with thealcoholic hydroxyl groups of the alicyclic alcohol that is added (seefollowing formula):

—COOH+HO—R —COO—R

[0224] The molecular weight (weight average molecular weight, Mw) of thealkali-soluble polymer described above may be varied within a wide rangedepending on the structure of the polymer, but it is normally preferredto be in the range of 2,000-1,000,000, and more preferably in the rangeof 3,000-50,000.

[0225] The alkali-soluble polymer to be used as the base resin for theinvention may be prepared using a polymerization process commonlyutilized in the field of polymer chemistry. For example, a(meth)acrylate-based copolymer can be successfully prepared by freeradical polymerization of the prescribed monomers required for itspreparation, by way of heating in the presence of a free radicalinitiator. As examples of free radical initiators there may be mentioned2,2′-azobisisobutyronitrile (AIBN) and dimethyl-2,2-azoisobisbutyrate(MAIB). Film-forming polymers other than (meth)acrylate-based polymersmay also be successfully prepared by similar commonly employedpolymerization processes.

[0226] With regard to the resist composition of this invention (secondinvention), its details including the composition, properties andproduction should be referred to the above descriptions with regard tothe resist composition of the first invention.

THIRD INVENTION

[0227] The resist composition and the method for forming a resistpattern according to the present invention (third invention) can bepracticed in various preferred embodiments as described in detail below.

[0228] The present invention relates to a chemically amplified negativeresist composition for forming a negative resist pattern on a treatedsubstrate, which can be developed with a basic aqueous solution.

[0229] This resist composition comprises (a) a film-forming firstpolymer having an alkali-soluble group, (b) a second polymer having onthe side chain an alcohol structure, and (c) PAG (photoacid generator)capable of generating an acid which can decompose by absorbing aradiation for forming an image and cause a reaction of the moiety havingan alcohol structure in the second polymer with the alkali-soluble groupof the first polymer, and the composition itself is soluble in a basicaqueous solution.

[0230] The mechanism of chemical amplification in the resist compositionof the present invention is described below. An example where a resinhaving vinyl phenol in the alkali-soluble moiety is used as the firstpolymer having an alkali-soluble group and a resin having on the sidechain an alcohol structure represented by formula (3) is used as thesecond polymer, is described below.

[0231] Upon exposure to an image-forming radiation for development afterthe formation of the resist film, the PAG in the resist compositionabsorbs the radiation and generates an acid. In a preferred embodiment,the resist film is heated after this exposure. When the resist film isheated, the acid previously generated catalytically acts and adehydration reaction of the tertiary alcohol takes place on the exposedarea of the film as shown below, as a result, the alkali-soluble groupof the polymer reacts with the phenol ring in the vicinity and theproperty thereof changes to be insoluble in a basic aqueous solution.

[0232] In this reaction, the cation after the dehydration reactioncauses an electrophilic displacement reaction with the hydroxyl group ofthe vinyl phenol or the carbon at the ortho-position thereof. In theformer, the reaction takes place directly with the alkali-soluble groupto reduce the alkali solubility and in the latter, the alkali solubilityis reduced by the strong hydrophobicity of the adamantyl group and thesteric hindrance thereof. More specifically, in the former case, areaction takes place to protect the hydroxyl group of the phenol ring inthe first polymer by the OH group as a reaction site of the alcohol inthe second polymer, so that the polarity of the exposed area changes andthe alkali solubility greatly decreases in the exposed area. In thelatter case, the phenol ring of the first polymer combines at theortho-position with the OH group of the alcohol in the second polymer tocause a steric hindrance, so that the alkali solubility decreases in theexposed area. As such, the alkali solubility greatly decreases in theexposed area to give a negative pattern. Either one of theprotection-type reaction or the alkali insolubility promoting reactionbased on the steric hindrance may take place. The reaction is preferablypredominated by the protection-type reaction because the change in thepolarity on the exposed area can be maximally used. The reactiondescribed in this example can be manly applied to the case where theexposure is performed using a KrF or EB light source.

[0233] Another example where an acrylic acid having a carboxylic acidunit is used for the alkali-soluble moiety of the first polymer and apolymer having on the side chain a compound of formula (3) is used asthe second polymer having an alcohol structure, is described below.Similarly to the above-described case, a dehydration reaction takesplace to cause a reaction with a carboxylic acid in the vicinity andthereby the alkali solubility of the first polymer decreases. Therefore,the alkali solubility extremely decreases in the exposed area to give anegative pattern. In this example, by the dehydration reaction ofalcohol, only a reaction of protecting the carboxylic acid is generated.The reaction described in this example can be manly applied to the casewhere the exposure is performed using an ArF light source.

[0234] As is apparent from the description in the foregoing pages, theresist composition of the present invention is amplification type ofcontaining a second polymer (additional resin) having an alcohol capableof reacting with the alkali-soluble group in the first polymer (baseresin) and re-generating a protonic acid by the reaction, therefore,high sensitivity can be achieved. After the functional group isprotected, due to the loss of the alkali-soluble group (change into anether or an ester), the exposed area of the resist film becomesalkali-insoluble, therefore, a negative pattern can be formed by thedevelopment with a basic aqueous solution. Incidentally, in the presentinvention, the pattern formation is performed by using the change in thepolarity generated in the polymer, therefore, a pattern free of swellingcan be obtained.

[0235] The alkali-soluble polymer used as the base material in theresist composition of the present invention, particularly when thepolymer is a terpolymer, may use a relatively strong alkali-solublegroup represented by carboxylic acid or phenol, for the first monomerunit and a weak alkali-soluble group having, for example, a lactone ringstructure, an acid anhydride or an imide ring structure, for the secondmonomer unit. If the case is so, the alkali solubility speed of the baseresin can be easily controlled to a preferred value by controlling thecontents of the strong alkali-soluble group and the weak alkali-solublegroup. For the third monomer unit, a compound containing a functionalgroup having etching resistance may be used and this is very preferredas the resist.

[0236] In the case where the alcohol structure contained in the secondpolymer of this resist composition is a tertiary alcohol, thedehydration reaction more readily occurs and this is very preferred.Other than this unit having an alcohol structure in the resin, acompound having an alcohol structure expected to undertake theabove-described reaction may be separately contained as an additive andsuch a material construction is also preferred. The structure of thisalcohol structure-containing compound is not particularly limited,however, on taking account of the contribution to the etchingresistance, a polynuclear alicyclic compound or a compound having abenzene ring is preferred. Furthermore, it is also very preferred thatthis alcohol structure-containing compound has, similarly to the sidechain of the second polymer, a tertiary alcohol structure which iseasily dehydrated by an acid.

[0237] The structure of the alkali-soluble first polymer used as thebase resin in the resist composition of the present invention is notparticularly limited as long as the above-described conditions,particularly, the condition that the polymer has an appropriate alkalisolubility speed, are satisfied. However, for obtaining dry etchingresistance comparable to the novolak resist, a polymer with an acrylate-or methacrylate-type monomer unit having a polynuclear alicyclichydrocarbon compound in the ester group, a vinyl phenol-type polymer, anN-substituted maleimide-type polymer or a styrene-type polymer ispreferably used. Among these, the acrylate- or methacrylate-type polymeris preferred when a light source having a wavelength in the deepultraviolet region, particularly at 220 nm or less is used, because theabsorption of light at that wavelength is small. In other words, in thecase of using a deep ultraviolet ray as the light source for exposure,it is preferred to use a polymer having a structure containing noaromatic ring which greatly absorbs the light in the deep ultravioletregion, or no chromophore having a large molar extinction coefficient,such as conjugate double bond.

[0238] Particularly, in the case of using a light source having anexposure wavelength in the ultrashort wavelength region, such as ArFexcimer laser, not only the dry etching resistance but also thetransparency at that wavelength (193 nm) are necessary, therefore, theabove-described polymer having an ester group containing a polynuclearalicyclic hydrocarbon structure capable of exhibiting high dry etchingresistance, represented by adamantyl group, bicyclo[2.2.1]octyl groupand norbornyl group, is preferably used.

[0239] The structure of the second polymer having an alcohol structure,which can be advantageously used in the practice of the presentinvention, is not particularly limited, but in the case of using apolymer having a relatively high molecular weight, care must given tothe compatibility so as not to cause phase separation from the baseresin. In order to cause no phase separation, a combination with apolymer having a molecular weight as low as an oligomer is preferred,but this does not apply in the case of a combination with a polymerhaving high compatibility represented by vinyl phenols and acrylicresin, and a combination with such a resin system is also preferred. Forthe main chain of the second polymer, the same monomer as in the firstpolymer may be used.

[0240] Examples of the alcohol structure on the side chain of the secondpolymer include the following structures, however, the present inventionis not limited thereto.

[0241] wherein R₁ to R₃, which may be the same or different, eachrepresents hydrogen atom or an alkyl group having from 1 to 6 carbonatoms which may have a linear or branched structure or a cyclicstructure, X represents hydrogen atom or a methyl group, Y is anarbitrary substituent containing hydrogen and represents an arbitraryalkyl group having from 1 to 6 carbon atoms, an alkoxycarbonyl group, aketone group, a hydroxyl group or a cyano group, and n represents aninteger of 1 to 6.

[0242] Examples of the second polymer having an alcohol structureincludes the following polymers, however, the present invention is notlimited thereto. In the following formulae, 1, mm and n each is a numberof monomer units (repeating units) necessary for obtaining theabove-described weight average molecular weight.

[0243] wherein Z is the moiety having an alcohol structure, X representshydrogen atom or an alkyl group, and R_(R) represents an arbitrary alkylgroup which may have a linear, branched or cyclic structure and whichmay contain an aromatic group in the substituent.

[0244] wherein X, Y, Z and R_(R) have the same meanings as definedabove, and R_(X) represents an arbitrary alkyl group which may have alinear, branched or cyclic structure and which may contain an aromaticgroup in the substituent.

[0245] wherein X, Y, Z, R_(R) and R_(X) have the same meanings asdefined above.

[0246] wherein X, Y, Z and R_(R) have the same meanings as describedabove.

[0247] In addition, diesters of malecic acid, fumaric acid, itaconicacid and other similar acids may be used in the formation of thepolymer, if desired.

[0248] As the compound having an alcohol structure, which is added tothe resist composition of the present invention, for example, thefollowing alcohol compounds can be advantageously used. Among thesealcohol structures, a tertiary alcohol is preferred.

[0249] wherein XX is hydrogen atom or an alkyl group having from 1 to 8carbon atoms which may have a linear, branched or cyclic structure andwhich may have a substituent, n is a number of 1 to 6, YY is anarbitrary substituent and represents an arbitrary alkyl group havingfrom 1 to 6 carbon atoms, an alkoxycarbonyl group, a ketone group, ahydroxyl group or a cyano group.

[0250] The first polymer having an alkali-soluble group and the secondpolymer having on the side chain an alcohol structure for use in thepresent invention can e prepared by a polymerization method commonlyused. For example, the polymer may be advantageously prepared by heatinga predetermined monomer component in the presence of AIBN(2,2′-azobisisobutyronitrile) as a free radical initiator.

[0251] The methacrylate polymer is well known to have high transparencyin the deep ultraviolet region, therefore, when for the first and secondpolymers, a structure not containing a chromophore having a large molarextinction coefficient in the vicinity of the exposure wavelength isappropriately selected, the resist obtained by combining these polymerswith an appropriate amount of PAG (photoacid generator) can have highsensitivity capable of advantageously coping with the exposure using adeep ultraviolet ray.

[0252] As described above, the alkali-soluble first polymer has analkali-soluble group which undertakes a reaction of insolubilizing thepolymer in a basic aqueous solution under the acid catalytic reaction inthe presence of an alcohol, and a protonic acid can be re-generated bythese reactions, therefore, high sensitivity can be achieved. After thereaction, the alkali-solubility decreases because the alkali-solublegroup disappears or due to the steric hindrance, as a result, theexposed area of the resist film becomes insoluble in a basic aqueoussolution and when the resist film is developed, the unexposed area isdissolved and a negative pattern is obtained. In this case, the changein the polarity generated in the base resin is used, therefore, apattern free of swelling can be obtained.

[0253] With regard to the resist composition of this invention (thirdinvention), its details including the composition, properties andproduction should be referred to the above descriptions with regard tothe resist composition of the first invention.

[0254] The resist composition of the present invention is furtherdescribed in the following items.

[0255] (1) A negative resist composition comprising a first polymerhaving an alkali-soluble group, a second polymer having on the sidechain an alcohol structure capable of reacting with the alkali-solublegroup, and a photoacid generator capable of generating an acid whichdecomposes by absorbing a radiation for forming an image and excites areaction between the alkali-soluble group of the first polymer and thealcohol of the second polymer, wherein the composition itself is solublein a basic aqueous solution and upon exposure to the radiation forforming an image, the exposed area becomes insoluble in the basicaqueous solution under the action of the photoacid generator.

[0256] (2) The negative resist composition as described in item 1,wherein the reaction excited by the photoacid generator is aprotection-type reaction of protecting the alkali-soluble group and/oran insolubility promotion-type reaction of promoting theinsolubilization of the alkali-soluble group in a basic aqueoussolution.

[0257] (3) The negative resist composition as described in item 1 or 2,wherein the alcohol structure is a tertiary alcohol structure.

[0258] (4) The negative resist composition as described in item 3,wherein the tertiary alcohol structure is represented by any one offormulae (1) to (4).

[0259] (5) The negative resist composition as described in any one ofitems 1 to 4, wherein the first polymer and the second polymer eachcomprises at least one monomer unit selected from the group consistingof acrylic acid-type, methacrylic acid-type, itaconic acid-type,vinylbenzoic acid-type, vinylphenol-type,bicyclo[2.2.1]hept-5-ene-2-carboxylic acid-type and N-substitutedmaleimide-type compounds and derivatives thereof.

[0260] (6) The negative resist composition as described in any one ofitems 1 to 5, wherein the content of the second polymer is from 0.1 to80 wt % based on the total polymer weight of the first polymer and thesecond polymer.

[0261] (7) The negative resist composition as described in any one ofitems 1 to 6, wherein the molecular weight of the second polymer is from500 to 100,000.

[0262] (8) The negative resist composition as described in any one ofitems 1 to 7, wherein a compound having an alcohol structure is furtheradded.

[0263] (9) The negative resist as described in item 8, wherein thecompound having an alcohol structure contains a tertiary alcoholstructure.

[0264] (10) The negative resist composition as described in item 8 or 9,wherein the compound having an alcohol structure has a boiling point ofat least 130° C.

[0265] (11) The negative resist composition as described in any one ofitems 8 to 10, wherein the compound having an alcohol structure containsan alicyclic structure or a polynuclear alicyclic structure.

[0266] (12) The negative resist composition as described in any one ofitems 8 to 11, wherein the compound having an alcohol structure containsat least one hydroxyl group, ketone group or alkyloxycarbonyl group.

[0267] (13) The negative resist composition as described in any one ofitems 1 to 12, wherein the first polymer further contains analkali-soluble group selected from the group consisting of a lactonering, an imide ring and an acid anhydride.

[0268] (14) The negative resist composition as described in any one ofitems 1 to 13, wherein the molecular weight of the first polymer is from2,000 to 1,000,000.

[0269] (15) The negative resist composition as described in any one ofitems 1 to 14, wherein the absorbance at the wavelength of the exposurelight source is 1.75/μm or less.

[0270] (16) The negative resist composition as described in any one ofitems 1 to 14, which contains a solvent selected from the solvent groupconsisting of ethyl lactate, methyl amyl ketone,methyl-3-methoxypropionate, ethyl-3-ethoxypropionate and propyleneglycol methyl ether acetate, as a sole solvent or a mixed solventcomprising a plurality of solvents.

[0271] (17) The negative resist composition as described in item 16,which further contains a solvent selected from the group consisting ofbutyl acetate, γ-butyrolactone, propylene glycol methyl ether and amixture thereof, as an auxiliary solvent.

[0272] (18) A method for forming a resist pattern, comprising a seriesof steps for coating the negative resist composition described in anyone of items 1 to 8 on a treated substrate to form a resist film, forselectively exposing the resist film by a radiation for forming an imageto accelerate the decomposition of the photoacid generator, and fordeveloping the exposed resist film with a basic aqueous solution.

FOURTH INVENTION

[0273] A preferred mode of the negative resist composition utilizing achemical amplification resist according to the present invention (fourthinvention) will now be explained.

[0274] First, the negative resist composition comprises, as componentsdirectly contributing to the reaction for formation of the resistpattern,

[0275] (1) a base resin composed of an alkali-soluble polymer,

[0276] (2) a photo acid generator capable of decomposing upon absorptionof image-forming radiation to generate an acid, and

[0277] (3) an alicyclic alcohol with a reactive site that can undergodehydration bonding reaction with the polymer of the base resin in thepresence of the acid generated by the photo acid generator.

[0278] The above components insolubilize the light exposed sections bythe reaction represented by formula (13). That is, the alicyclic alcoholhas a highly polar group such as an alcoholic hydroxyl group in themolecule. The alicyclic alcohol is preferably a tertiary alcohol with astereochemically fixed structure. This is because the bond produced bythe reaction between the alkali-soluble group and tertiary alcohol ofthe base resin, resulting for example in an ether structure, isirreversibly fixed due to its stereochemical structure. Throughout thisspecification, a condition in which the situation prior to the reactioncannot be readily regenerated due to stereochemistry will be referred toas being “stereochemically fixed”. A tertiary alcohol is preferredbecause it has high reactivity and more readily undergoes dehydrationreaction. Such substances react with the polar groups of the base resin(phenolic hydroxyl groups, etc.) in the presence of an acid catalyst,resulting in stable esterification or etherification.

[0279] Then, diligent research by the present inventors has shown thatthe molecular weight distribution value is no greater than 1.5, andpreferably no greater than 1.3 for the base resin in the negative resistcomposition of the invention. Using a base resin with a weight averagemolecular weight in the prescribed range can give even highersensitivity and resolution.

[0280] A smaller molecular weight distribution of the base resin usedcan produce the insolubilization reaction at the exposed sections in amore preferred fashion. This is assumed to be because reduction of themolecular weight distribution of the base resin to achieve a uniformmolecular weight results in almost simultaneous insolubilization of eachmolecule. When a negative resist composition employing such amonodisperse resin as the base resin is exposed to light, even if thebase resin is directly crosslinked by the image-forming radiation, theproportion is exceedingly minimal and therefore the molecular weightdistribution of those sections even after the insolubilization reactionwill not exceed 2.

[0281] Furthermore, a resist composition with even higher sensitivityand resolution can be obtained if there are no sections with a weightaverage molecular weight of 2,000 or less, and preferably all sectionsare in the range of 3,000 to 20,000. If the goal is to achieve a stillhigher sensitivity and higher resolution resist, it is recommended forthe weight average molecular weight to be in the range of 5,000 to10,000.

[0282] When the base resin is monodispersed, it may be blended with apolymer having a different weight average molecular weight. That is,even blending with polymers containing no portions with a weight averagemolecular weight of not more than 2,000 and having different weightaverage molecular weights of, for example, 5,000, 6,000 and 7,000 toform the base resin, will still allow the same effect as a monodispersecondition.

[0283] Since most monodisperse resins have a very high dissolution ratein developers, it may be prepared as a copolymer of another monomer (forexample, styrene, methoxystyrene, etc.) and vinylphenol to lower thedissolution rate. For a lower dissolution rate of the monodisperseresin, a small amount of novolac or the like with a comparatively slowerdissolution rate may be included.

[0284] Incidentally, a resist with high sensitivity and high resolutioncan also be achieved by controlling each of the individual molecules ofthe polymer composing the base resin so that no low molecular weightpolymers are included with an (actual) molecular weight of not more than2000. The present inventors have concluded that the resist sensitivityis reduced because the low molecular weight components essentially donot contribute to the insolubilizing effect.

[0285] When using a base resin with no more than 10 wt %, and preferablyno more than 3 wt % of its content consisting of low molecular weightcomponents of molecular weight below 2000, it is possible to form asatisfactory resist composition with practical high sensitivity and highresolution. As mentioned above, the base resin is preferably amonodisperse system, but a satisfactory negative resist composition canalso be obtained simply by keeping a minimal content of low molecularweight components.

[0286] The base resin described above may be a polymer that is commonlyused in the prior art, and phenol-based resins are preferred. Asphenol-based resins there may be used the novolac types such asphenol-novolac and cresol-novolac, or the vinyl types such aspolyvinylphenol; it is preferred to use polyvinylphenol whichfacilitates preparation of the molecular weight distribution and cuttingof the low molecular weight portions.

[0287] Preparation of the molecular weight distribution and cutting ofthe low molecular weight portions of the base resin may be accomplishedusing separation methods such as living anion polymerization or gelpermeation chromatography (GPC).

[0288] The effect due to monodispersion of the base resin is seen evenwith alicyclic alcohols having a plurality of hydroxyl groups, but it isparticularly notable in the polarity-altering reaction systemrepresented by formula (3) above, which involves no crosslinkingreaction. That is, the negative-conversion (insolubilization) reactionin the resist of the invention is based primarily on a polarity changeand there is virtually no increase in molecular weight. Consequently, noswelling occurs with development. When the aforementioned monodisperseresin is applied as the base resin, the molecular weight distribution ofthe insolubilized sections after light exposure is no greater than 2even considering direct crosslinking by the image-forming radiationresulting in an increased molecular weight.

[0289] The alicyclic alcohol which is the third reaction component andthe photoacid generator which is the second component will now beexplained.

[0290] The alicyclic alcohol used may be one having one of the followingstructures.

[0291] The alicyclic alcohol is used at about 2 parts to 60 parts, andpreferably 15 parts to 40 parts, with respect to 100 parts of the baseresin. If the amount of the alicyclic alcohol is too small, the polaritychange occurring with the reaction will be lower making it impossible toachieve the essential contrast as a negative resist. On the other hand,if the amount of the alicyclic alcohol is too large, a greater exposuredose will be necessary to complete the substituent reaction, creating apoorly cost-effective situation. In addition, when the alicyclic alcoholis added in such a large amount, the thermal properties of the resistcomposition as a whole may be inferior and other undesirable problemssuch as precipitation during resist coating may occur.

[0292] With regard to the resist composition of this invention (fourthinvention), its details including the composition, properties andproduction should be referred to the above descriptions with regard tothe resist composition of the first invention.

[0293] The resist composition of the present invention is furtherdescribed in the following items.

[0294] (1) A negative resist composition wherein the molecular weightdistribution of the sections rendered insoluble by light exposure isbetween 1 and 2 inclusive.

[0295] (2) A negative resist composition according to (1), characterizedby containing a base resin which comprises an alkali-soluble polymer, aphoto acid generator which is capable of decomposing upon absorption ofimage-forming radiation to generate an acid, and an alicyclic alcoholwith a reactive site that can undergo dehydration bonding reaction withthe alkali-soluble group of the base resin in the presence of the acidgenerated by the photo acid generator.

[0296] (3) A negative resist composition according to (1) or (2),characterized in that the molecular weight distribution of the baseresin is between 1 and 1.5 inclusive.

[0297] (4) A negative resist composition according to (2) or (3),characterized in that the weight average molecular weight of the baseresin is at least 2000.

[0298] (5) A negative)resist composition according to (4), characterizedin that the weight average molecular weight of the base resin is from3,000 to 20,000.

[0299] (6) A negative resist composition containing a base resin whichcomprises an alkali-soluble polymer, a photo acid generator which iscapable of decomposing upon absorption of image-forming radiation togenerate an acid, and an alicyclic alcohol with a reactive site that canundergo dehydration bonding reaction with the alkali-soluble group ofthe base resin in the presence of the acid generated by the photo acidgenerator,

[0300] characterized in that no more than 10 wt % thereof consists ofcomponents with a molecular weight of not more than 2000 in the baseresin.

[0301] (7) A negative resist composition according to any of (1) to (6),characterized in that the base resin contains a phenol-based compound.

[0302] (8) A negative resist composition according to (7), characterizedin that the base resin is polyvinylphenol or a copolymer of vinylphenoland another monomer.

[0303] (9) A negative resist composition according to any of (1) to (8),characterized in that the alicyclic alcohol has an adamantane structure.

[0304] (10) A negative resist composition according to any of (1) to(9), characterized in that the alicyclic alcohol has a tertiary alcoholstructure with a stereochemically fixed structure.

[0305] (11) A negative resist composition according to (10),characterized in that the tertiary alcohol is a 1-adamantanol or aderivative thereof.

[0306] (12) A negative resist composition according to any of (1) to(11), characterized in that the photo acid generator is one selectedfrom the group consisting of onium salts, halogenated organic substancesand sulfonic acid esters.

[0307] (13) A negative resist composition according to (12),characterized in that the onium salt is selected from the groupconsisting of compounds (A) to (D) mentioned above.

[0308] (14) A negative resist composition according to (12),characterized in that the halogenated organic substance is a triazinewith a halogen in the structure or an isocyanurate with a halogen in thestructure.

[0309] (15) A negative resist pattern forming method, which comprisesthe series of steps including coating a negative resist compositionaccording to any of (1) to (14) onto a target substrate, selectivelyexposing the formed resist film to image-forming radiation that caninduce decomposition of the photo acid generator of the resistcomposition, and developing the exposed resist film with a basic aqueoussolution.

[0310] According to yet another aspect of the invention, there isprovided a method for forming resist patterns, and particularly negativeresist patterns, on target substrates using any one of the resistcompositions of the present invention (first to fourth inventions). Asalready explained above, the negative resist pattern forming method ofthe invention is characterized by comprising the following steps:

[0311] coating a negative resist composition according to the inventiononto a target substrate,

[0312] selectively exposing the formed resist film to image-formingradiation that can induce decomposition of the photo acid generator ofthe resist composition, and

[0313] developing the exposed resist film with a basic aqueous solution.

[0314] In the resist pattern forming method of the invention, the resistfilm formed on the target substrate is preferably subjected to heattreatment (or baking) after the selective exposure to image-formingradiation. Specifically, according to the method of the invention, theresist film may be prebaked before exposure, and then heat treated aspost exposure baking (PEB) after exposure and before development, asexplained above. The heat treatment may be successfully carried outaccording to a common method.

[0315] The negative resist pattern forming method of the invention maygenerally be carried out in the following manner.

[0316] First, the resist composition of the invention is coated onto atarget substrate to form a resist film. The target substrate may be asubstrate that is commonly used for manufacture of semiconductor devicesand other such devices, a few examples of which are silicon substrates,glass substrates, non-magnetic ceramic substrates, compoundsemiconductor substrates and alumina and other insulating crystalsubstrates. If necessary, an additional layer such as a silicon oxidelayer, a wiring metal layer, an interlayer insulating film, a magneticfilm or the like may be present on these substrates, or differentwirings, circuits and the like may be built therein. These substratesmay be subjected to hydrophobic treatment by common methods to increasethe cohesion of the resist film therewith. As an example of anappropriate hydrophobic treatment agent there may be mentioned1,1,1,3,3,3-hexamethyldisilazane (HMDS).

[0317] As mentioned above, the resist composition is usually coated ontothe target substrate in the form of a resist solution. The coating ofthe resist solution may be accomplished by a common technique such asspin coating, roll coating, dip coating or the like, but spin coating isparticularly useful. The thickness of the resist film is notparticularly restricted, but is normally preferred to be in the range ofabout 0.1-200 μm, and in the case of exposure with a KrF or ArF excimerlaser, for example, the recommended range is about 0.1-1.5 μm. Thethickness of the resist film to be formed can be varied within a widerange depending on such factors as the purpose for which the resist filmwill be used.

[0318] The resist film coated onto the substrate is preferably prebakedat a temperature of about 60-180° C. for about 30-120 seconds prior toits selective exposure with the image-forming radiation. The prebakingmay be carried out using common heating means for resist processes. Asexamples of suitable heating means there may be mentioned a hot plate,an infrared heating oven or the like.

[0319] The prebaked resist film is then selectively exposed toimage-forming radiation with a conventional light exposure apparatus.Suitable light exposure apparatuses include commercially availableultraviolet ray (far ultraviolet ray, deep ultraviolet ray) exposureapparatuses, X-ray exposure apparatuses, electron beam exposureapparatuses, excimer steppers and the like. The light exposureconditions may be selected as appropriate for the procedure. As wasmentioned above, excimer lasers (KrF lasers with a wavelength of 248 nm,ArF lasers with a wavelength of 193 nm and other lasers) areparticularly advantageous as light exposure sources for the invention.Throughout the present specification, therefore, the term “radiation”will mean light from these various types of light sources, i.e.ultraviolet rays, far ultraviolet rays, deep ultraviolet rays, anelectron beam (EB), X-rays, laser light and the like. The selectivelight exposure results in absorption of the radiation by thefilm-forming polymer in the light exposed sections of the resist film bythe mechanism described above, resulting in its decomposition and acidgeneration.

[0320] The exposed resist film is then subjected to post exposure baking(PEB) to cause an alkali-soluble group-protecting reaction catalyzed bythe acid. The conditions for the post exposure baking are notparticularly limited so long as they cause and adequately promote theintended protecting reaction, and for example, the baking may be carriedout under the same conditions as the previous prebaking. For example,the post exposure baking temperature may be about 60-180° C., andpreferably about 100-150° C., with a baking time of about 30-120seconds. The post exposure baking conditions are preferably adjustedaccording to the desired pattern size, form, etc.

[0321] After completion of the post exposure baking, the exposed resistfilm is developed in a basic aqueous solution as the developer. For thedevelopment there may be used a common developing apparatus such as aspin developer, dip developer, spray developer or the like. The type ofbasic aqueous solution that may be advantageously used as the developerin this case is an aqueous solution containing the hydroxide of a metalof Group I or II of the Periodic Table, typical of which is potassiumhydroxide, or an aqueous solution of an organic base containing no metalions, such as a tetraalkylammonium hydroxide. The basic aqueous solutionis more preferably an aqueous solution of tetramethylammonium hydroxide(TMAH) or tetraethylammonium hydroxide (TEAH). The basic aqueoussolution may also contain an additive such as a surfactant to enhancethe developing effect. The development results in dissolution andremoval of the unexposed sections of the resist film, leaving a resistpattern of only the exposed sections on the substrate. In other words,according to the method of the invention it is possible to obtain anintricate negative resist pattern. Of particular importance is that aresist pattern according to the invention may be advantageously used forformation of wiring patterns with narrow line widths of 0.15 μm orsmaller.

[0322] In addition, the present invention resides in a process for theproduction of electronic devices using the negative resist compositionsof the present invention described above, and the electronic devicesthus produced. Note that the “electronic devices” means a wide varietyof electronic apparatuses including semiconductor devices and magneticrecording heads and thus they should not be restricted to the electronicdevices having the specific structure. Further, as will be appreciatedfrom the above description, the negative resist composition of thepresent invention used in the production of the electronic devicesaccording to the present invention includes all of the negative resistcompositions according to the first to fourth inventions of the presentinvention.

[0323] The production process of electronic devices according to thepresent invention is characterized by using as a masking means a resistpattern formed from the negative resist composition of the presentinvention to selectively removing the underlying target substrate suchas substrate, thinfilm and coating, thereby forming a predeterminedfunctional element layer. Preferably, etching is used to selectivelyremove the target substrate.

[0324] As described above in connection with the formation of resistpatterns, the underlying substrate, thinfilm and like to be selectivelyor patternwise removed upon etching is generally referred herein to“target substrate” (or “treated substrate”). That is, the targetsubstrate means all of the substrates, thinfilms and coatings to beetched in the production of electronic devices such as semiconductordevices and magnetic heads. Although not restricted to, examples ofsuitable target substrates include a semiconductor substrate such assilicon substrate and GaAs substrate, an electrically insulatingcrystalline substrate such as compound semiconductor and alumina(Al₂O₃), and the following thinfilms or coatings:

[0325] PSG, TEOS, SiON, TiN, amorphous carbon, metal silicide such asAl—Si, Al—Si—Cu and WSi, polysilicon (Poly-Si), amorphous silicon, SiO₂,GaAs, TiW and others.

[0326] In addition to the above thinfilms and coatings, (giant)magnetoresistive layers including Cu, Co, FeMn, NiFe, LaSrMnO and othersare also included in the scope of the target substrate.

[0327] According to the production process of the electronic devicesaccording to the present invention, the target substrate remains as apatterned substrate, thinfilm or coating, and such a patterned productis referred herein to as a “functional element layer”, because it canshow the predetermined functions and effects in the produced electronicdevices.

[0328] Preferably, the production process of electronic devicesaccording to the present invention can be carried out by the followingsteps:

[0329] coating the negative resist composition of the present inventiononto the target substrate,

[0330] selectively exposing the formed resist film to image-formingradiation that can induce decomposition of the photo acid generator ofthe resist composition,

[0331] developing the exposed resist film with a basic aqueous solutionto form a resist pattern, and

[0332] etching the target substrate in the presence of the resistpattern as a masking means to form a functional element layer.

[0333] As described hereinbefore, the image-forming radiation used inthe exposure step of the resist film is not restricted to the specificone, and include a wide variety of light sources used in the resistprocess in the production of semiconductor devices and other devices.Typical examples of suitable light sources include Hg lamp such asg-line and i-line, KrF, ArF and other excimer lasers, electron beam andX-rays.

[0334] According to the present invention, there is also provided anelectronic device comprising at least one patterned substrate, thinfilmor coating (functional element layer) in any suitable position(s) of thedevice, the functional element layer being formed using as a maskingmeans a resist pattern formed from the negative resist composition ofthe present invention, in the selective removal process of the targetsubstrate.

[0335] Next, the electronic device of the present invention and itsproduction process will be further described referring to, particularly,semiconductor devices and magnetic heads.

[0336] The semiconductor device manufacturing process of the inventionis preferably carried out using the following steps:

[0337] coating of a resist composition according to the invention onto atarget substrate,

[0338] selectively exposing the formed resist film to image-formingradiation capable of inducing decomposition of the photo acid generatorin the resist composition,

[0339] developing the exposed resist film with a basic aqueous solutionto form a resist pattern, and

[0340] etching the underlying target substrate for its removal, usingthe resist pattern as the masking means.

[0341] According to this semiconductor device manufacturing process, thestep of forming the resist film, the step of selective light exposurewith radiation and the step of forming the resist pattern may each besuccessfully accomplished in the manner described above.

[0342] The subsequent step of etching the resist pattern may beaccomplished by wet etching or dry etching according to a commontechnique, but considering the recent progress in micronization and thetrend toward environmental friendliness, dry etching is moreadvantageous. As is well known, dry etching accomplishes etching of atarget substrate in a gas phase, and examples of suitable dry etchingtechniques are plasma etching techniques, such as reactive ion etching(RIE), reactive ion beam etching (RIBE) and ion beam etching. These dryetching techniques may be carried out under prescribed conditions usingcommercially available etching apparatuses.

[0343] For most purposes, the resist pattern formed by the method of theinvention can be advantageously used as masking means for selectiveetching removal of an underlying target substrate in the mannerdescribed above, but so long as the resist pattern satisfies theprescribed conditions in terms of required properties, it can also beused as one of the elements of a semiconductor device, for example, asthe insulating film itself.

[0344] The term “semiconductor device” as used throughout the presentspecification refers to semiconductor devices in the general sense andis not particularly limited. As is generally recognized in the technicalfield, typical semiconductor devices include common semiconductorintegrated circuits such as ICs, LSIs and VLSIs, as well as otherrelated devices.

[0345] More specifically, a MOS transistor, which is a typical instanceof a semiconductor device, may be manufactured according to theinvention in the following manner for illustration.

[0346] First, a gate oxidation film, polysilicon film and WSi film thatare necessary for construction of a transistor are formed in that orderas thin films on a silicon substrate. The thin films may be formed usinga common thin film forming technique such as thermal oxidation, chemicalvapor deposition (CVD) or the like.

[0347] Next, the resist composition of the invention is coated onto theWSi film to form a resist film of the prescribed thickness. The resistfilm is selectively exposed to radiation suitable for the patterning,and it is then developed in a basic aqueous solution for dissolution andremoval of the exposed sections. More specifically, the series of stepsto this point may be carried out in the manner described above forformation of the resist pattern.

[0348] In order to form a gate electrode structure, the resist patternformed in the manner described above is used as a mask for simultaneousdry etching of the underlying WSi film and the polysilicon film underit. After thus forming a gate electrode comprising a polysilicon filmand a WSi film, phosphorus is injected by ion injection to form an N⁻diffusion layer for an LDD structure.

[0349] Next, after the resist pattern used in the previous step isreleased off from the electrode, an oxidation film is formed over theentire surface of the substrate by CVD, and the formed CVD oxidationfilm is subjected to anisotropic etching to form a side wall on the sideof the gate electrode formed by the polysilicon film and WSi film. TheWSi film and side wall are then used as a mask for ion injection to forman N⁺ diffusion layer, thereby coating the gate electrode with a thermaloxidation film.

[0350] Finally, an interlayer insulation film is formed over the entireuppermost layer of the substrate by CVD, and the resist composition ofthe invention is again coated thereover and selectively etched to form ahole pattern (resist pattern) in the wiring formation sections. Theresist pattern is used as a mask for etching of the underlyinginterlayer insulation film, to form contact holes. The formed contactholes are then filled in with aluminum (Al) wiring. An N-channelintricate MOS transistor is thus completed.

[0351] In addition to the semiconductor described above, the presentinvention include magnetic recording heads as one embodiment of theelectronic devices. That is, using the negative resist composition ofthe present invention in the resist process, it becomes possible toprovide high performance thinfilm magnetic recording heads. The magneticrecording heads can be advantageously used in the production of magneticrecording and reading devices such as magnetic disk devices and magnetictape devices.

[0352] The production process of the magnetic heads according to thepresent invention can be preferably carried out by the following steps:

[0353] coating the negative resist composition of the present onto thetarget substrate,

[0354] selectively exposing the formed resist film to image-formingradiation that can induce decomposition of the photo acid generator ofthe resist composition,

[0355] developing the exposed resist film with a basic aqueous solutionto form a resist pattern, and

[0356] etching the target substrate in the presence of the resistpattern as a masking means to form a functional element layer.

[0357] Magnetic heads will be further described. Recently, magneticrecording and reading devices such as magnetic disk devices are beingchanged to a small size along with increase of the recording density,and, to satisfy the requirements in such recent devices, amagnetoresistive head (so-called “MR head”) capable of converting achange of the signal magnetic field in the magnetic recording medium toa change of the electric resistance based on the magnetoresistiveeffects are widely used as a reproducing or reading head in suchdevices. Among the MR heads, the attractive one is a GMR head, i.e.,giant magnetoresistive head, since it can exhibit high output withoutrelying upon a moving speed of the magnetic recording medium. Inparticular, spin valve-type MR heads utilizing the magnetoresistiveeffects of the spin valve has been already practically used, becausethey can be relatively easily produced and, comparing with other MRheads, they can provide higher variation rate of the electric resistanceat a low magnetic field. In the production of these and other magneticheads, the negative resist compositions of the present invention can beadvantageously used, since such resist composition can be fabricatedinto finely patterned film which is suitable as functional element(s) ofthe head.

[0358] To assist in further understanding of the magnetic head, the spinvalve-type magnetic head will be further described with regard to thestructure and production thereof. Note, however, that the magnetic headsof the present invention should not be restricted to the followingheads.

[0359] As is well-known in the art, generally, the spin valve headcomprises a magnetoresistive film (spin valve film) and, electricallyconnected thereto, a pair of electrodes which define a signal detectionarea and apply a signal detecting electric current to the signaldetection area, and a pair of longitudinal bias magnetic fieldapplication films which apply longitudinal bias magnetic field to thespin valve head. The longitudinal bias magnetic field application filmsare generally formed from a hard magnetic film such as CoPt and CoCrPt.The application of the longitudinal bias magnetic field applicationfilms of hard magnetic material to those other than the magnetosensitivearea (signal detection area) of the spin valve head in such a mannerthat such films are disposed in both sides or upper sides of the headcan inhibit formation of Barkhausen's noise due to movement of themagnetic wall of free magnetic layer of the spin valve film, thusenabling to obtain stable reading profile without noise.

[0360] Further, generally, the spin valve film having a laminatedstructure which comprises a free magnetic layer, a nonmagneticinterlayer, a pinned magnetic layer and a regular anti-ferromagneticlayer, in sequence, on an underlayer. The application of such a layerstructure is effective to control an angle by the magnetizationdirections of two magnetic layers (free magnetic layer and pinnedmagnetic layer) laminated through the nonmagnetic interlayer, therebychanging the electric resistance as desired.

[0361] More particularly, the spin valve film is generally formed on analutic substrate, i.e., substrate comprising a TiC base having appliedon a surface thereof an alumina film. The underlayer as the lowermostlayer may be formed from a Ta coating an the like, because the Tacoating can give a good crystalinity to the free magnetic layer. The Tacoating or other underlayers can be generally formed using aconventional process such as sputtering, vacuum deposition and chemicalvapour deposition (CVD).

[0362] The free magnetic layer may be formed from any soft magneticmaterial. For example, generally used CoFe alloy may be used in theformation of the free magnetic layer. Although not restricted to, thefree magnetic layer may be preferably produced(Co_(y)Fe_(100−y))_(100−x) Z_(x) alloy having a face-centered cubiclattice structure in which Z represents any elements other Co and Fe,preferably boron B or carbon C, and x and y each is atomic percentage(at %), because heads having high sensitivity to magnetic field and ahigh heat resistance can be produced. The free magnetic field ispreferably formed as a double layer structure than as a single layer, inview of the resulting properties. The free magnetic layer can begenerally formed by using the conventional process such as sputtering.

[0363] In the spin valve film, it is preferred to sandwich a nonmagneticinterlayer with the free magnetic layer and a pinned magnetic layerwhich will be described below. As the nonmagnetic interlayer, generally,nonmagnetic metal such as copper (Cu) may be used. The Cu interlayer canbe formed using the conventional process such as sputtering.

[0364] As in the formation of the free magnetic layer, the pinnedmagnetic layer may be formed from any soft magnetic material. That is,CoFe alloy may be used in the formation of the pinned magnetic layer,however, it may be preferably formed (Co_(y)Fe_(100−y))_(100−x) Z_(x)alloy having a face-centered cubic lattice structure in which Zrepresents any elements other Co and Fe, preferably boron B or carbon C,and x and y each is atomic percentage (at %), because heads having highoutput, high sensitivity to magnetic field and a high heat resistancecan be produced. The pinned magnetic layer can be generally formed byusing the conventional process such as sputtering.

[0365] A regular anti-ferromagnetic layer is formed over the pinnedmagnetic layer. The anti-ferromagnetic layer is generally formed fromFeMn, NiMn, PtMn, PdMn, PdPtMn, CrMn, IrMn and the like, for example. Asin the layers mentioned above, the anti-ferromagnetic layer can begenerally formed by using the conventional process such as sputtering.

[0366] Generally, the spin valve film has a cap layer as the uppermostlayer. The cap layer may be formed from, for example, Ta coating. As inthe layers mentioned above, the cap layer can be generally formed byusing the conventional deposition process.

[0367] The spin valve heads may be produced in accordance with anyconventional methods. Particularly, according to the present invention,the above-mentioned functional element layers can be produced as anexactly and finely fabricated patter having the desired profile, whenthe resist process using the negative resist composition of the presentinvention is introduced into any desired step(s) of the head productionprocess. The following is one example of producing a spin valve headaccording to the present invention.

[0368] First, tantalum (Ta) is deposited through sputtering on an aluticsubstrate to form a Ta underlayer. Next, the following layers aredeposited, in sequence, by using a lift-off process, ion milling processand any other conventional processes, through an electrode (for example,Au) over the Ta underlayer exclusive of the magnetosensitive portion ofthe signal detection area of the head to be produced:

[0369] Underlayer, for example, Ta/NiFe-based alloy or NiFe-based alloysuch as NiFe, NiFeCr, NiFeNf and NiFeMo;

[0370] Longitudinal bias magnetic field application layer, for example,anti-ferromagnetic material such as PtMn, PdPtMn, NiMn, CrMn and CrPtMn;and

[0371] Underlayer, for example, NiFe-based alloy.

[0372] Next, to completely remove any contamination substances(so-called “contamination layer”) from a surface of the resulting head,an uppermost surface of the Ta underlayer and NiFe underlayer issubjection to a cleaning process using sputter-etching, ion milling orother methods.

[0373] After completion of the above cleaning process, a free magneticlayer, a nonmagnetic interlayer, a pinned magnetic layer and a regularanti-ferromagnetic layer is deposited in the described order to form aspin valve film. Each layer may be formed by using sputtering, vapourdeposition or CVD process, for example.

[0374] Thereafter, to obtain a spin valve film with the desired pattern,the spin valve layer is deposited over a full surface of thelongitudinal bias magnetic field application layer, followed by forminga patterned resist layer from the negative resist composition of thepresent invention and then removing the undesired spin valve film withion milling, for example.

[0375] After formation of the patterned spin valve film, a pair ofelectrodes is formed over the spin valve film exclusive of themagnetosensitive portion of the signal detection area of the head. Theelectrodes may be preferably formed upon lift-off fabrication of the Aulayer. Of course, any other electrode material may be used in place ofAu, if desired. The spin valve head is thus produced.

EXAMPLES

[0376] The present invention will now be explained by way of examplesrelating to preparation of resist compositions, formation of resistpatterns and production of electronic devices including semiconductordevices and magnetic recording heads. It is to be understood, however,that the scope of the invention is not limited by these examples.

Example 1

[0377] A 3-hydroxy-adamantyl methacrylate/y-butyrolacton-2-ylmethacrylate/methacrylic acid copolymer (compositional ratio: 6:1:3) wasdissolved in propyleneglycol methyl ether acetate (PGMEA) to make a 15wt % solution. To this copolymer solution there was addedγ-butyrolactone as a co-solvent to 9 wt % with respect to the copolymer.Triphenylsulfonium trifluoromethanesulfonate was added to the solutionto 2 wt % with respect to the copolymer, and thoroughly dissolvedtherein. After filtering the resulting resist solution with a 0.2 μmTeflon™ membrane filter, it was spin coated at 2000 rpm onto anHMDS-treated silicon substrate and prebaked at 110° C. for 60 seconds.This produced a resist film with a thickness of 0.5 μm. After exposingthe resist film to a KrF excimer laser stepper (NA=0.45) it wassubjected to post exposure baking (PEB) at 120° C. for 60 seconds,developed with a 2.38% tetramethylammonium hydroxide (TMAH) aqueoussolution and rinsed with deionized water for 60 seconds. Measurement ofthe resolution of the resulting negative resist pattern confirmed thatan exposure dose of 14.0 mJ/cm² allowed resolution of a 0.25 μmline-and-space (L/S) pattern. Also, no swelling at all was found in theresist pattern.

[0378] In order to evaluate the dry etching resistance of the resist,the silicon substrate coated with the resist in this manner to 1 μmthickness was placed in a parallel plate RIE apparatus for CF₄ sputteretching under the following conditions: Pμ=200 W, pressure=0.02 Torr,CF₄ gas=100 sccm, for a period of 5 minutes. As shown in the tablebelow, the etching rate was confirmed to be 689 Å/min.

[0379] For comparison, the dry etching resistance with the commerciallyavailable novolac resist, Nagase Positive Resist NPR-820 (product ofNagase Industries) and polymethyl methacrylate (PMMA) was evaluated inthe same manner as above, giving the following results. Tested resistEtching rate (Å/min) Rate ratio NPR-820 530 1.00 PMMA 805 1.52 Example 1689 1.30

[0380] As seen from the results shown above, the dry etching resistanceof the resist composition of the invention was close to that of thenovolac resist, and much superior to that of PMMA.

Example 2

[0381] The procedure described in Example 1 was repeated, but for thisexample an ArF excimer laser exposure apparatus (NA=0.55) was usedinstead of the KrF excimer laser stepper, as the exposure apparatus. Inthis example, an exposure dose of 6.2 mJ/cm² allowed resolution of a0.20 μm L/S pattern. The other properties of the obtained negativeresist pattern were also satisfactorily comparable to the properties ofExample 1.

Example 3

[0382] The procedure described in Example 1 was repeated, but for thisexample an electron beam exposure apparatus (output=50 kV) was usedinstead of the KrF excimer laser stepper, as the exposure apparatus. Inthis example, an exposure dose of 10 μC/cm² allowed resolution of a 0.15μm L/S pattern. The other properties of the obtained negative resistpattern were also satisfactorily comparable to the properties of Example1.

Example 4

[0383] A 3-hydroxy-adamantyl methacrylate/y-butyrolacton-2-ylmethacrylate/methacrylic acid copolymer (compositional ratio: 6:1:3) wasdissolved in PGMEA to make a 15 wt % solution. To this copolymersolution there was added 20 wt % of 1-adamantanol (as an alcoholstructure-containing compound) and 10 wt % of γ-butyrolactone (as aco-solvent), with respect to the copolymer. Diphenyliodoniumtrifluoromethanesulfonate was added to the solution to 2 wt % withrespect to the copolymer, and thoroughly dissolved therein. Afterfiltering the resulting resist solution with a 0.2 μm Teflon™ membranefilter, it was spin coated at 2000 rpm onto an HMDS-treated siliconsubstrate and prebaked at 110° C. for 60 seconds. This produced a resistfilm with a thickness of 0.5 μm. After exposing the resist film to anArF excimer laser exposure apparatus (NA=0.55) it was subjected to postexposure baking (PEB) at 130° C. for 60 seconds, developed with a 2.38%TMAH aqueous solution and rinsed with deionized water for 60 seconds.Measurement of the resolution of the resulting negative resist patternconfirmed that an exposure dose of 3.4 mJ/cm² allowed resolution of a0.18 μm L/S pattern. Also, no swelling at all was found in the resistpattern.

[0384] Evaluation of the dry etching resistance of the resist accordingto the method described in Example 1 confirmed an etching rate of 678Å/min, as shown in the table below. The table also shows the etchingrates for the Nagase positive resist NPR-820 and PMMA. Tested resistEtching rate (Å/min) Rate ratio NPR-820 530 1.00 PMMA 805 1.52 Example 4678 1.28

[0385] As seen from the results shown above, the dry etching resistanceof the resist composition of the invention was close to that of thenovolac resist, and much superior to that of PMMA.

Example 5

[0386] A 3-hydroxy-adamantyl methacrylate/y-butyrolacton-2-ylmethacrylate/methacrylic acid copolymer (compositional ratio: 6:1:3) wasdissolved in PGMEA to make a 15 wt % solution. To this copolymersolution there was added 20 wt % of 3-hydroxybicyclo[2.2.2]octane (as analcohol structure-containing compound) and 10 wt % of γ-butyrolactone(as a co-solvent), with respect to the copolymer. Diphenyliodoniumtrifluoromethanesulfonate was added to the solution to 2 wt % withrespect to the copolymer, and thoroughly dissolved therein. Afterfiltering the resulting resist solution with a 0.2 μm Teflon™ membranefilter, it was spin coated at 2000 rpm onto an HMDS-treated siliconsubstrate and prebaked at 110° C. for 60 seconds. This produced a resistfilm with a thickness of 0.5 μm. After exposing the resist film to anArF excimer laser exposure apparatus (NA=0.55) it was subjected to postexposure baking (PEB) at 120° C. for 60 seconds, developed with a 2.38%TMAH aqueous solution and rinsed with deionized water for 60 seconds.Measurement of the resolution of the resulting negative resist patternconfirmed that an exposure dose of 4.0 mJ/cm² allowed resolution of a0.18 μm L/S pattern. Also, no swelling at all was found in the resistpattern.

Example 6

[0387] The procedure described in Example 5 was repeated, but for thisexample an electron beam exposure apparatus (output=50 kV) was usedinstead of the ArF excimer exposure apparatus. In this example, anexposure dose of 8 μC/cm² allowed resolution of a 0.15 μm L/S pattern.This resist pattern was also free of any swelling.

Example 7

[0388] A 3-hydroxy-adamantyl methacrylate/y-butyrolacton-2-ylmethacrylate/methacrylic acid copolymer (compositional ratio: 6:1:3) wasdissolved in PGMEA to make a 15 wt % solution. To this copolymersolution there was added 15 wt % of 2,6-dimethyl-2-heptanol (as analcohol structure-containing compound) and 10 wt % of γ-butyrolactone(as a co-solvent), with respect to the copolymer. Diphenyliodoniumtrifluoromethanesulfonate was added to the solution to 2 wt % withrespect to the copolymer, and thoroughly dissolved therein. Afterfiltering the resulting resist solution with a 0.2 μm Teflon™ membranefilter, it was spin coated at 2000 rpm onto an HMDS-treated siliconsubstrate and prebaked at 110° C. for 60 seconds. This produced a resistfilm with a thickness of 0.5 μm. After exposing the resist film to anArF excimer laser exposure apparatus (NA=0.55) it was subjected to postexposure baking (PEB) at 110° C. for 60 seconds, developed with a 2.38%TMAH aqueous solution and rinsed with deionized water for 60 seconds.Measurement of the resolution of the resulting negative resist patternconfirmed that an exposure dose of 5.2 mJ/cm² allowed resolution of a0.20 μm L/S pattern. Also, no swelling at all was found in the resistpattern.

Example 8

[0389] After polymerizing 3-hydroxy-adamantyl methacrylate and4-acetoxystyrene at a charging ratio of 1:9, the polymer was furthertreated with an alkali solution for solvolysis of the acetyl groups. Theresulting 3-hydroxy-adamantyl methacrylate/vinylphenol copolymer(compositional ratio: 1:9) was dissolved in PGMEA to make a 15 wt %solution. To this solution there was added triphenylsulfoniumtrifluoromethanesulfonate to 5 wt % with respect to the copolymer, andit was thoroughly dissolved therein. After filtering the resultingresist solution with a 0.2 μm Teflon™ membrane filter, it was spincoated at 2000 rpm onto an HMDS-treated silicon substrate and prebakedat 110° C. for 60 seconds. This produced a resist film with a thicknessof 0.5 μm. After exposing the resist film to a KrF excimer laser stepper(NA=0.45) it was subjected to post exposure baking (PEB) at 120° C. for60 seconds, developed with a 2.38% TMAH aqueous solution and rinsed withdeionized water for 60 seconds. Measurement of the resolution of theresulting negative resist pattern confirmed that an exposure dose of 6.8mJ/cm² allowed resolution of a 0.25 μm L/S pattern. Also, no swelling atall was found in the resist pattern.

[0390] Evaluation of the dry etching resistance of the resist accordingto the method described in Example 1 confirmed an etching rate of 620Å/min, as shown in the table below. The table also shows the etchingrates for the Nagase positive resist NPR-820 and PMMA. Tested resistEtching rate (Å/min) Rate ratio NPR-820 530 1.00 PMMA 805 1.52 Example 8541 1.02

[0391] As seen from the results shown above, the dry etching resistanceof the resist composition of the invention was very close to that of thenovolac resist, and much superior to that of PMMA.

Example 9

[0392] The procedure described in Example 8 was repeated, but for thisexample an electron beam exposure apparatus (output=50 kV) was usedinstead of the KrF excimer laser stepper. In this example, an exposuredose of 8 μC/cm² allowed resolution of a 0.12 μm L/S pattern. The otherproperties of the obtained negative resist pattern were alsosatisfactorily comparable to the properties of Example 8.

Example 10

[0393] A 3-hydroxy-adamantyl methacrylate/vinylphenol copolymer(compositional ratio: 1:9) was dissolved in PGMEA to make a 15 wt %solution. To this copolymer solution there was added 20 wt % of1-adamantanol (as an alcohol structure-containing compound), withrespect to the copolymer. Triphenylsulfonium trifluoromethanesulfonatewas added to the solution to 5 wt % with respect to the copolymer, andit was thoroughly dissolved therein. After filtering the resultingresist solution with a 0.2 μm Teflon™ membrane filter, it was spincoated at 2000 rpm onto an HMDS-treated silicon substrate and prebakedat 110° C. for 60 seconds. This produced a resist film with a thicknessof 0.5 μm. After exposing the resist film to a KrF excimer laser stepper(NA=0.45) it was subjected to post exposure baking (PEB) at 110° C. for60 seconds, developed with a 2.38% TMAH aqueous solution and rinsed withdeionized water for 60 seconds. Measurement of the resolution of theresulting negative resist pattern confirmed that an exposure dose of 6.4mJ/cm² allowed resolution of a 0.25 μm L/S pattern. Also, no swelling atall was found in the resist pattern.

[0394] Evaluation of the dry etching resistance of the resist accordingto the method described in Example 1 confirmed an etching rate of 599Å/min, as shown in the table below. The table also shows the etchingrates for the Nagase positive resist NPR-820 and PMMA. Tested resistEtching rate (Å/min) Rate ratio NPR-820 530 1.00 PMMA 805 1.52 Example10 519 0.98

[0395] As seen from the results shown above, the dry etching resistanceof the resist composition of the invention was comparable to that of thenovolac resist, and much superior to that of PMMA.

Example 11

[0396] The procedure described in Example 8 was repeated, but for thisexample 20 wt % of 3-hydroxybicyclo[2.2.2]octane (as an alcoholstructure-containing compound) was also included with respect to thecopolymer during preparation of the copolymer solution. After lightexposure using the KrF excimer laser stepper, post exposure baking (PEB)was carried out at 110° C. for 60 seconds. Measurement of the resolutionof the resulting negative resist pattern confirmed that an exposure doseof 7.2 mJ/cm² allowed resolution of a 0.25 μm L/S pattern. The otherproperties of the obtained negative resist pattern were alsosatisfactorily comparable to the properties of Example 8.

Example 12

[0397] The procedure described in Example 10 was repeated, but for thisexample an electron beam exposure apparatus (output=50 kV) was usedinstead of the KrF excimer laser stepper, and the post exposure baking(PEB) was carried out at 120° C. for 60 seconds. In this example, anexposure dose of 7 μC/cm² allowed resolution of a 0.11 μm L/S pattern.The other properties of the obtained negative resist pattern were alsosatisfactorily comparable to the properties of Example 10.

Example 13

[0398] The procedure described in Example 11 was repeated, but for thisexample an electron beam exposure apparatus (output=50 kV) was usedinstead of the KrF excimer laser stepper, and the post exposure baking(PEB) was carried out at 120° C. for 60 seconds. In this example, anexposure dose of 8 μC/cm² allowed resolution of a 0.12 μm L/S pattern.The other properties of the obtained negative resist pattern were alsosatisfactorily comparable to the properties of Example 11.

Example 14

[0399] A vinyl benzoate/3-hydroxy-adamantyl methacrylate copolymer(compositional ratio: 3:7) was dissolved in PGMEA to make a 15 wt %solution. To this copolymer solution there was added 20 wt % of1-adamantanol (as an alcohol structure-containing compound) and 10 wt %of γ-butyrolactone (as a co-solvent), with respect to the copolymer.Triphenylsulfonium trifluoromethanesulfonate was added to the solutionto 2 wt % with respect to the copolymer, and thoroughly dissolvedtherein. After filtering the resulting resist solution with a 0.2 μmTeflon™ membrane filter, it was spin coated at 2000 rpm onto anHMDS-treated silicon substrate and prebaked at 110° C. for 60 seconds.This produced a resist film with a thickness of 0.5 μm. After exposingthe resist film to a KrF excimer laser stepper (NA=0.45) it wassubjected to post exposure baking (PEB) at 130° C. for 60 seconds,developed with a 2.38% TMAH aqueous solution and rinsed with deionizedwater for 60 seconds. Measurement of the resolution of the resultingnegative resist pattern confirmed that an exposure dose of 17.5 mJ/cm²allowed resolution of a 0.28 μm L/S pattern. Also, no swelling at allwas found in the resist pattern.

Example 15

[0400] The procedure described in Example 14 was repeated, but for thisexample an electron beam exposure apparatus (output=50 kV) was usedinstead of the KrF excimer laser stepper, and the post exposure baking(PEB) was carried out at 120° C. for 60 seconds. In this example, anexposure dose of 10 μC/cm² allowed resolution of a 0.12 μm L/S pattern.This resist pattern was also free of any swelling.

Example 16

[0401] The following substances were provided as resist components.

[0402] Base resin 1

[0403] Polyvinylphenol (weight average molecular weight: 12,000;distribution: 2.0)

[0404] Additive 1 (as alicyclic alcohol)

[0405] PAG1 (as photoacid generator)

[0406] Triphenylsulfonium trifluoromethanesulfonate

[0407] A resist solution was prepared by dissolving base resin 1,additive 1 and PAG1 in ethyl lactate in a weight ratio of 10:2:1. Afterfiltering the resulting resist solution with a 0.2 μm Teflon™ membranefilter, it was spin coated at 2000 rpm onto an HMDS-treated siliconsubstrate and prebaked at 110° C. for 2 minutes. This produced a resistfilm with a thickness of 0.8 μm. The resist film was subjected topattern exposure with the following three types of exposure apparatuses:

[0408] i-ray exposure apparatus (wavelength: 365 nm)

[0409] KrF excimer laser stepper (NA=0.45, wavelength: 248 nm)

[0410] Electron beam exposure apparatus (output: 50 kV) The exposurepattern was a 0.4 μm line-and-space (L/S) with i-rays, a 0.25 μm L/Swith the KrF laser and a 0.25 L/S with the electron beam. Aftersubsequent post-exposure baking (PEB) at 120° C. for 2 minutes, it wasdeveloped with a 2.38% tetramethylammonium hydroxide (TMAH) aqueoussolution for 30 seconds and rinsed with deionized water for 60 seconds.Evaluation of the resolution of the resulting negative resist patterngave the following results.

[0411] i-rays: exposure dose=22 mJ/cm², resolution={circumflex over (∘)}

[0412] KrF laser: exposure dose=16 mJ/mc², resolution={circumflex over(∘)}

[0413] Electron beam: exposure dose=7 μC/cm², resolution={circumflexover (∘)}

[0414] The resolution was evaluated based on the following 4-levelscale.

[0415] {circumflex over (∘)}: Rectangular cross-sectional shape.Difference between dimensions of pattern top and dimension of patternbottom less than 1% of exposure pattern dimensions.

[0416] ◯: Roughly rectangular cross-sectional shape. Difference betweendimensions of pattern top and dimension of pattern bottom within 1-5% ofexposure pattern dimensions.

[0417] Δ: Somewhat tapered cross-sectional shape. Difference betweendimensions of pattern top and dimension of pattern bottom greater than5% but less than 10% of exposure pattern dimensions.

[0418] X: Tapered cross-sectional shape. Difference between dimensionsof pattern top and dimension of pattern bottom greater than 10% ofexposure pattern dimensions.

[0419] The evaluation results are listed in Table 1 below for comparisonwith other resist compositions.

[0420] In order to next evaluate the dry etching resistance of theresist, a silicon substrate coated with the resist to 1 μm thickness inthe same manner as described above was placed in a parallel plate RIEapparatus for CF₄ sputter etching under the following conditions: Pμ=200W, pressure=0.02 Torr, CF₄ gas=100 sccm, for a period of 5 minutes. Theetching rate was found to be 689 Å/min, thus confirming excellent dryetching resistance.

Examples 17-39

[0421] The procedure described in Example 16 was repeated, but for theseexamples the base resin, additive (alicyclic alcohol) and PAG (photoacidgenerator) were changed as shown in Table 1. The components used inthese examples were as follows.

[0422] Base resin 2

[0423] Methacrylate/methyl methacrylate copolymer (copolymerizationratio: 35:65, weight average molecular weight: 10,000; distribution:2.3)

[0424] Table 1 below summarizes the results of evaluating the resistcompositions for each example.

Comparative Examples 1-4

[0425] The procedure described in Example 16 was repeated, but forcomparison in these comparative examples, three different commerciallyavailable negative melamine-based resists (detailed composition unknown)and a pinacol-based resist prepared for comparison were used, as shownin Table 1. The pinacol used in the pinacol-based resist had thefollowing structure.

[0426] Table 1 summarizes the results of evaluating the resistcompositions for each comparative example. TABLE 1 i-rays (365 nm) KrF(248 nm) Electron ray (50 kV) Exposure Exposure Exposure Component doseResolu- dose Resolu- dose Resolu- Example Resin Additive PAG (mJ/cm²)tion (mJ/cm²) tion (μC/cm²) tion 16 1 1 1 22 ⊚ 16 ⊚ 7 ⊚ 17 1 2 23 ⊚ 16 ⊚6 ⊚ 18 1 3 30 ⊚ 16 ⊚ 4 ⊚ 19 2 1 14 ⊚ 15 ⊚ 6 ⊚ 20 2 2 14 ⊚ 14 ⊚ 5 ⊚ 21 23 14 ⊚ 15 ◯ 2 ⊚ 22 1 2 1 24 ⊚ 18 ⊚ 10 ⊚ 23 1 2 25 ⊚ 15 ⊚ 10 ◯ 24 1 3 30⊚ 16 ◯ 7 ⊚ 25 2 1 16 ◯ 17 ◯ 8 ⊚ 26 2 2 15 ⊚ 15 ⊚ 6 ⊚ 27 2 3 14 ⊚ 15 ⊚ 6◯ 28 1 3 1 22 ⊚ 15 ⊚ 8 ◯ 29 1 2 22 ◯ 20 ◯ 8 ⊚ 30 1 3 25 ◯ 20 ⊚ 8 ⊚ 31 21 16 ⊚ 18 ⊚ 7 ⊚ 32 2 2 16 ⊚ 15 ⊚ 3 ◯ 33 2 3 20 ⊚ 17 ◯ 5 ⊚ 34 1 4 1 30 ◯18 ⊚ 6 ⊚ 35 1 2 25 ⊚ 17 ⊚ 10 ⊚ 36 1 3 30 ◯ 20 ⊚ 10 ⊚ 37 2 1 12 ⊚ 15 ⊚ 5◯ 38 2 2 14 ⊚ 14 ◯ 8 ⊚ 39 2 3 12 ⊚ 15 ⊚ 7 ⊚ Comp. Ex. 1 1 melamine 1 30◯ 25 Δ 25 Δ Comp. Ex. 2 1 melamine halogen-based 35 ◯ 20 ◯ 30 Δ Comp.Ex. 3 1 melamine ester-based 32 Δ 18 Δ 30 Δ Comp. Ex. 4 1 pinacol 1 40 Δ25 Δ 10 ◯

[0427] The results shown in Table 1 indicate that the resistcompositions of the invention gave higher sensitivity and much moresatisfactory resolution than the prior art products (the resists of thecomparative examples). This is attributed to the greater polarity changewhich facilitated negative conversion of the resist at the exposedsections, thus creating a greater dissolution rate difference.

Example 40

[0428] To polyvinylphenol produced by Maruzen Sekiyu K.K., 7 wt % of ahomopolymer (molecular weight: 2,000) of 3-hydroxyadamantyl methacrylatewas added. The resulting mixture was dissolved in PGMEA (propyleneglycol methyl ether acetate) to prepare a resin solution. To thesolution obtained, 5 wt % of triphenylsulfoniumtrifluoromethanesulfonate was added and thoroughly dissolved. Thethus-obtained resist solution was filtered through a 2.0 μm teflonmembrane filter, spin-coated on a silicon substrate subjected to an HMDStreatment, and pre-baked at 110° C. for 60 seconds to form a 0.5μm-thick resist film. This resist film was exposed by a KrF excimerlaser stepper (NA=0.45), baked at 120° C. for 60 seconds, developed witha 2.38% tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 14.0 mJ/cm², a resolution of0.25 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 41

[0429] Using the resist solution prepared in Example 40, a 0.5 μm-thickresist film was formed on a silicon substrate similarly subjected to anHMDS treatment. This resist film was exposed by an EB exposure apparatus(50 kV), baked at 120° C. for 60 seconds, developed with a 2.38%tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 12 μC/cm², a resolution of0.15 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 42

[0430] To the resin solution prepared in Example 40, 10 wt % of1-adamantanol was added based on the weight of polyvinylphenol and 5 wt% of diphenyliodonium trifluoromethanesulfonate was added based on theresin to prepare a resist solution. This resist solution was spin-coatedon a silicon substrate subjected to an HMDH treatment and pre-baked at110° C. for 60 seconds to form a 0.5 μm-thick resist film. This resistfilm was exposed by a KrF excimer laser exposure apparatus, baked at120° C. for 60 seconds, developed with a 2.38% tetramethylammoniumhydroxide (TMAH) developer, and rinsed with deionized water. With anexposure amount of 8 μC/cm², a resolution of 0.25 μmL/S was obtained. Inthis resist pattern, swelling was not generated.

Example 43

[0431] To the resin solution prepared in Example 40, 10 wt % of3-hydroxybicyclo[2.2.2]octane and 10 wt % of γ-butyrolactone as anauxiliary solvent were added, each based on the weight of resin.Furthermore, 5 wt % of diphenyliodonium trifluoromethanesulfonate wasadded based on the resin to prepare a resist solution. This resistsolution was spin-coated on a silicon substrate subjected to an HMDHtreatment and pre-baked at 110° C. for 60 seconds to form a 0.5 μm-thickresist film. This resist film was exposed by a KrF excimer laserexposure apparatus, baked at 120° C. for 60 seconds, developed with a2.38% tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 9 mJ/cm², a resolution of0.25 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 44

[0432] The resist film of Example 43 was exposed by an EB exposureapparatus (50 kV), baked at 120° C. for 60 seconds, developed with a2.38% tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 15 μC/cm², a resolution of0.15 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 45

[0433] 3-Hydroxyadamantyl methacrylate and 4-acetoxystyrene were chargedat a charge ratio of 2:8 to synthesize a base resin. The resin obtainedwas treated with an alkali solution to cause soluvolysis of the acetylgroup, thereby obtaining a 3-hydroxyadamantyl methacrylate-vinylphenolcopolymer (molecular weight: 4,500). To polyvinylphenol produced byMaruzen Sekiyu, 15 wt % of the copolymer obtained was added and themixture was dissolved in PGMEA (propylene glycol methyl ether acetate).To this solution, 5 wt % of triphenylsulfoium trifluoromethanesulfonatewas added and thoroughly dissolved. The thus-obtained resist solutionwas filtered through a 0.2 μm teflon membrane filter, spin-coated on asilicon substrate subjected to an HMDS treatment, and pre-baked at 110°C. for 60 seconds to form a 0.5 μm-thick resist film. This resist filmwas exposed by a KrF excimer laser stepper (NA=0.45), baked at 120° C.for 60 seconds, developed with a 2.38% tetramethylammonium hydroxide(TMAH) developer, and rinsed with deionized water. With an exposureamount of 12.0 mJ/cm², a resolution of 0.25 μmL/S was obtained. In thisresist pattern, swelling was not generated.

Example 46

[0434] The resist film of Example 45 was exposed by an EB exposureapparatus (50 kV), baked at 120° C. for 60 seconds, developed with a2.38% tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 18 μC/cm², a resolution of0.12 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 47

[0435] To the resin solution prepared in Example 45, 5 wt % of1-adamantanol was added based on the weight of resin and 5 wt % oftriphenylsulfonium trifluoromethanesulfonate was added to prepare aresist solution. This resist solution was filtered through a 0.2 μmteflon membrane filter, spin-coated on a silicon substrate subjected toan HMDH treatment and pre-baked at 110° C. for 60 seconds to form a 0.5μm-thick resist film. This resist film was exposed by a KrF excimerlaser stepper (NA=0.45), baked at 110° C. for 60 seconds, developed witha 2.38% tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 10 μC/cm², a resolution of0.25 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 48

[0436] To the resin solution prepared in Example 45, 8 wt % of3-hydroxybicyclo[2.2.2]octane was added based on the weight of resin toprepare a resist solution. This resist solution was filtered through a0.2 μm teflon membrane filter, spin-coated on a silicon substratesubjected to an HMDH treatment and pre-baked at 110° C. for 60 secondsto form a 0.5 μm-thick resist film. This resist film was exposed by aKrF excimer laser stepper (NA=0.45), baked at 120° C. for 60 seconds,developed with a 2.38% tetramethylammonium hydroxide (TMAH) developer,and rinsed with deionized water. With an exposure amount of 9 mJ/cm², aresolution of 0.25 μmL/S was obtained. In this resist pattern, swellingwas not generated.

Example 49

[0437] The resist film of Example 47 was exposed by an EB exposureapparatus (50 kV), baked at 120° C. for 60 seconds, developed with a2.38% tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 12 μC/cm², a resolution of0.12 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 50

[0438] The resist film of Example 48 was exposed by an EB exposureapparatus (50 kV), baked at 120° C. for 60 seconds, developed with a2.38% tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 15 μC/cm², a resolution of0.12 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 51

[0439] Ethyl vinylbenzoate and 4-hydroxyadamantyl acrylate were chargedat a charge ratio of 7:3 to synthesize a resin (molecular weight:3,000). The resin obtained was added to a monodisperse polyvinylphenol(molecular weight: 5,000) in an amount of 15 wt %, and the resultingmixture was dissolved in PGMEA (propylene glycol methyl ether acetate)to prepare a resin solution. To the solution obtained, 5 wt % oftriphenylsulfoium trifluoromethanesulfonate was added and thoroughlydissolved. The thus-obtained resist solution was filtered through a 0.2μm teflon membrane filter, spin-coated on a silicon substrate subjectedto an HMDS treatment, and pre-baked at 110° C. for 60 seconds to form a0.5 μm-thick resist film. This resist film was exposed by a KrF excimerlaser stepper (NA=0.45), baked at 130° C. for 60 seconds, developed witha 2.38% tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 17.5 mJ/cm², a resolution of0.28 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 52

[0440] To the resin solution prepared in Example 51, 10 wt % of1-adamantanol was added based on the weight of resin and 10 wt % ofγ-butyrolactone was added. To this solution obtained, 5 wt % oftriphenylsulfonium trifluoromethanesulfonate was added and thoroughlydissolved. The thus-obtained resist solution was filtered through a 0.2μm teflon membrane filter, spin-coated on a silicon substrate subjectedto an HMDH treatment and pre-baked at 110° C. for 60 seconds to form a0.5 μm-thick resist film. This resist film was exposed by a KrF excimerlaser stepper (NA=0.45), baked at 120° C. for 60 seconds, developed witha 2.38% tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 12 mJ/cm², a resolution of0.25 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 53

[0441] The resist film of Example 52 was exposed by an EB exposureapparatus (50 kV), baked at 120° C. for 60 seconds, developed with a2.38% tetramethylammonium hydroxide (TMAH) developer, and rinsed withdeionized water. With an exposure amount of 15 μC/cm², a resolution of0.12 μmL/S was obtained. In this resist pattern, swelling was notgenerated.

Example 54

[0442] The following (I) polyvinylphenol-based base resins, (II)photoacid generators and (III) alicyclic alcohols were provided ascomponents for the resist compositions in the examples.

[0443] (I) Base resins (polyvinylphenol)

[0444] 1) Weight average molecular weight: 12,000 Molecular weightdistribution: 2.0 (prior art)

[0445] 2) Weight average molecular weight: 3,200 Molecular weightdistribution: 1.15

[0446] 3) Weight average molecular weight: 5,000 Molecular weightdistribution: 1.11

[0447] 4) Weight average molecular weight: 10,000 Molecular weightdistribution: 1.11

[0448] 2)+3)+4) above.

[0449] The above components were combined in order and dissolved inethyl lactate to prepare a resist solution, and this was compared with acommercially available negative resist composition (melamine-based) anda pinacol-based resist prepared for comparison. The resist compositionof the examples and the pinacol-based resist were prepared in a ratio ofbase resin:alicyclic alcohol:photoacid generator=10:2:1 (weight ratio).After filtering each resulting resist solution with a 0.2 μm Teflon™membrane filter, it was spin coated at 2000 rpm onto an HMDS-treatedsilicon substrate and prebaked at 100° C. for 2 minutes. The pinacolused was the one mentioned under “Prior Art” above. The three types ofmelamine-based resists used were commercially marketed ones andtherefore their detailed compositions were unknown.

[0450] The resist film obtained above was subjected to pattern exposurewith the following three types of exposure apparatuses:

[0451] (1) i-ray exposure apparatus (wavelength: 365 nm)

[0452] (2) KrF excimer laser stepper (NA=0.45, wavelength: 248 nm)

[0453] (3) Electron beam exposure apparatus (output: 50 kV)

[0454] The exposure pattern was a 0.4 μm line-and-space (L/S) withi-rays, a 0.25 μm L/S with the KrF laser and a 0.2 μm L/S with theelectron beam. After subsequent post-exposure baking (PEB) at 120° C.for 2 minutes, it was developed with a 2.38% tetramethylammoniumhydroxide (TMAH) aqueous solution for 30 seconds and rinsed withdeionized water for 60 seconds. The resolution of each of the resultingnegative resist patterns was evaluated. The results are shown in Table 2below. TABLE 2 i-rays (365 nm) KrF (248 nm) Electron ray (50 kV)Exposure Exposure Exposure dose Resolu- dose Resolu- dose Resolu- ResinAdditive PAG (mJ/cm²) tion (mJ/cm²) tion (μC/cm²) tion Prior art 1 1 122 ◯ 16 ◯ 7 ◯ Non- 1 2 23 ◯ 16 ◯ 6 ◯ mono- disperse Invention 2 1 10 ⊚ 8⊚ 4 ⊚ resists 2 2 11 ⊚ 8 ⊚ 3 ⊚ 3 1 12 ⊚ 9 ⊚ 4 ⊚ 3 2 9 ⊚ 8 ⊚ 4 ⊚ 4 1 15 ⊚12 ⊚ 3 ⊚ 4 2 7 ⊚ 10 ⊚ 2 ⊚ 5 1 8 ⊚ 8 ⊚ 2 ⊚ 5 2 8 ⊚ 9 ⊚ 2 ⊚ Prior art 1 21 30 Δ 18 ◯ 6 ◯ Non 1 2 25 ◯ 17 ◯ 10 ◯ mono- disperse Invention 2 1 15 ⊚6 ⊚ 4 ⊚ resists 2 2 14 ⊚ 7 ◯ 3 ⊚ 3 1 12 ⊚ 12 ⊚ 2 ⊚ 3 2 10 ⊚ 9 ⊚ 2 ⊚ 4 115 ⊚ 8 ⊚ 5 ⊚ 4 2 14 ⊚ 9 ⊚ 2 ⊚ 5 1 14 ⊚ 6 ⊚ 2 ⊚ 5 2 13 ⊚ 9 ⊚ 4 ⊚ Com- 1melamine 1 30 Δ 25 X 25 X mercially 1 melamine halogen-based 35 Δ 20 Δ30 X available 1 melamine ester-based 32 X 18 X 30 X resists for 1pinacol 1 40 X 25 X 10 Δ comparison

[0455] The symbols ({circumflex over (∘)}, ◯, Δ and X) for the 4-levelevaluation scale used in Table 2 are explained below.

[0456] {circumflex over (∘)}: Rectangular cross-sectional shape of theformed pattern. Difference between dimensions of pattern top anddimension of pattern bottom less than 0.5% of exposure patterndimensions.

[0457] ◯: Roughly rectangular cross-sectional shape of the formedpattern. Difference between dimensions of pattern top and dimension ofpattern bottom within 0.5-1% of exposure pattern dimensions.

[0458] Δ: Somewhat tapered cross-sectional shape of the formed pattern.Difference between dimensions of pattern top and dimension of patternbottom within 1-5% of exposure pattern dimensions.

[0459] X: Tapered cross-sectional shape of the formed pattern.Difference between dimensions of pattern top and dimension of patternbottom greater than 5% of exposure pattern dimensions.

[0460] The results shown in Table 1 confirm that the negative resistcompositions of the examples exhibited higher sensitivity and higherresolution than the common prior art products also tested.

[0461] Preferred examples of the invention have been described above,but it should be noted that the present invention is not limited tothese specific embodiments, and different modifications and variationsmay also be applied while retaining the gist of the invention as laidout in the claims.

Example 55

[0462] Production of MOS Transistor

[0463] As is illustrated in FIG. 1A, a gate oxide layer 2 was formed ona surface of silicon substrate 1, followed by forming a polysiliconlayer (Poly-Si layer) 3 thereon with a CVD process. After formation ofthe Poly-Si layer 3, n-type impurities such as phosphorus was introducedto make a low resistance area. Then, a WSi layer 4 was formed with asputtering process (CVD process and others may be used in place of thesputtering process).

[0464] Next, as illustrated in FIG. 1B, to make patterning of thePoly-Si layer 3 and the WSi layer 4, the negative resist composition ofthe present invention was coated over a full surface of the WSi layer 4formed in the previous step. After prebaking thereof, the resist layer 5was exposed in a KrF excimer exposure apparatus, and then was subjectedto post-exposure baking (PEB). The exposed resist layer 5 was alkalinedeveloped to obtain resist patterns of 0.25 μm width. Anisotropicetching using the resist pattern as a mask was made to etch the WSilayer 4 and the Poly-Si layer 3 in sequence. A gate electrode consistingof the etched Poly-Si layer 3 and WSi layer 4. Thereafter, phosphorouswas introduced through ion implantation process to form a N⁻ diffusionlayer of LDD structure. The resist layer 5 was removed with a removingsolution, after the pattern shown in FIG. 1B was obtained.

[0465] Following the formation of the gate electrode, as shown in FIG.1C, an oxide layer 7 was fully formed with the CVD process.

[0466] Then, as is shown in FIG. 1D, the oxide layer 7 wasanisotropically etched to form a side wall 8 consisting of the WSi layer4 and the Poly-Si layer 3 on the gate electrode side. Ion implantationwas then made in the presence of the WSi layer 4 and the side wall 8 asa mask to form a N⁺ diffusion layer 9.

[0467] Thereafter, to activate the N⁺ diffusion layer, thermal treatmentwas made in an atmosphere of nitrogen, followed by heating inan-atmosphere of oxygen. As shown in FIG. 1E, the gate electrode wascovered with a thermal oxidation layer 10.

[0468] Following the formation of the thermal oxidation layer 10, as isshown in FIG. 1F, an interlayer insulating layer 11 was formed with theCVD process, and the interlayer insulating layer 11 was patterned usingagain the negative resist composition of the present invention. That is,the resist composition of the present invention was fully coated overthe interlayer insulating layer 11, and the resist layer (not shown) wasprebaked, exposed in a ArF excimer exposure apparatus and post-exposurebaked. Upon alkaline development, hole-like resist patterns of 0.20 μmwidth were produced. Anisotropic etching using the resist patterns as amask was made to form a contact holes in the interlayer insulating layer11. An aluminum (Al) wiring 12 was deposited in the contact holes. Asillustrated, a finely fabricated N-channel MOS transistor 20 wasproduced.

Example 56

[0469] Production of Thinfilm Magnetic Head

[0470] As shown in FIG. 2A, a shield layer 22 of FeN and a gapinsulating layer 23 of silicon oxide were deposited, in sequence, on analutic substrate 21, followed by forming a magnetoresistive layer 24having a thickness of 400 nm from FeNi with a sputtering process. Themagnetoresistive layer 24 was coated with conventional PMGI resist(Microlithography Chemical Co., USA) to form a lower resist layer 25,and the lower resist layer 25 was overcoated with the negative resistcomposition of the present invention to form an upper resist layer 26.

[0471] After the double-structured resist layer was formed in accordancewith the above-mented method, the upper resist layer 26 was prebaked,exposed in a KrF excimer exposure apparatus and post-exposure baked.Upon alkaline development, resist patterns of 0.25 μm width wereobtained. At the same time with the alkaline development, the lowerresist layer 25 was isotropically developed to form an undercut profileof the resist patterns shown in FIG. 2B.

[0472] Then, as shown in FIG. 2C, ion milling was made using the resistpatterns as a mask to conduct etching, thereby obtaining the taperedmagnetoresistive layer 24.

[0473] Next, a TiW layer 27 was formed with sputtering on a full surfaceof the substrate 21. A thickness of the thus formed TiW layer 27 was 800nm.

[0474] After the formation of the TiW layer 27 was completed, the lowerresist layer 25 as well as the overlying upper resist layer 26 and TiWlayer 27 were removed in accordance with a lift-off process. As shown inFIG. 2E, the TiW layer 27 were exposed.

[0475] Thereafter, although not shown, the magnetoresistive layer 24 andthe TiW layer 27 were patterned in accordance with the manner, describedabove, using the negative resist composition of the present invention.As shown in FIG. 2F, an electrode 28 and a magnetoresistive (MR) element29 were thus formed.

[0476] Following the above step, as shown in FIG. 2G, a gap insulatinglayer 31 having a thickness of 50 nm was formed from silicon oxide(SiO₂).

[0477] Next, as shown in FIG. 2H, a shield layer 32 of FeNi having athickness of 3.5 μm, a gap layer 33 of Al₂O₃ having a thickness of 0.5μm and a FeNi layer 34 having a thickness of 3 μm were formed, insequence, over the gap insulating layer 31. Then, to form a writingmagnetic pole upon patterning of the FeNi layer 34, the negative resistcomposition of the present invention was coated over a full surface ofthe FeNi layer 34 to form a resist layer 36.

[0478] As a final step of the illustrated process, the resist layer 36formed on the FeNi layer 34 was prebaked, exposed in a KrF excimerexposure apparatus and post-exposure baked. Upon alkaline development,fine resist patterns having opening in the site corresponding to thewriting magnetic pole to be formed. Isotropic etching of the FeNi layer34 using the resist patterns as a mask was made. As shown in FIG. 2I, athinfilm magnetic head 40 having the writing magnetic pole 35 was thusproduced.

EFFECT OF THE INVENTION

[0479] The effects of the present invention (first to fourth inventions)are summarized as follows.

[0480] (1) As explained above, when a resist composition according tothe present invention is used it is possible to use a basic aqueoussolution as the developer, thus allowing formation of intricate negativeresist patterns with practical sensitivity and no swelling. A resistcomposition according to the invention is also suitable for deepultraviolet image-forming radiation, typical of which are KrF and ArFexcimer lasers, and has excellent dry etching resistance. Using a resistaccording to the invention can give a high polarity difference betweenthe exposed sections and unexposed sections, to form intricate negativepatterns with high sensitivity, high contrast and high resolution.

[0481] (2) As explained above, by using a resist composition accordingto the invention it is possible to achieve a large polarity differencebetween the exposed sections and unexposed sections, in order to formintricate negative resist patterns with high sensitivity, high contrastand high resolution. Moreover, basic aqueous solutions may be used asdevelopers for formation of the resist patterns. The resist compositionof the invention can also be applied to image-forming radiation sourcesin the deep ultraviolet range, typical of which are KrF excimer lasers,as well as electron beams, while also exhibiting high dry etchingresistance. By using resists according to the invention it is possibleto form intricate wiring patterns at high yields for the manufacture ofsemiconductor devices such as LSIs.

[0482] (3) As clearly known from the detailed description above,according to the inventions described in claims 1 to 8, the secondpolymer having on the side chain an alcohol structure is presenttogether with the first polymer having an alkali-soluble group, so thatdue to the excitation of the photoacid generator by the exposure, thealcohol undertakes a protection reaction or the like of insolubilizingthe alkali-soluble group in a basic aqueous solution and thereby thepolarity of the exposed area is greatly changed. Therefore, a novelnegative resist composition can be provided, which can form a dense andfine negative resist pattern free of swelling with practically usablesensitivity. Furthermore, the negative resist composition of the presentinvention can have high sensitivity as compared with conventional resistcompositions and therefore the pattern can be formed using the change inthe polarity, so that high contrast and high resolution can be easilyattained.

[0483] In addition, according to the method for forming a resistpattern, the above-described novel negative resist composition is used,therefore, a resist pattern free of swelling can be formed with highsensitivity, high contrast and high resolution.

[0484] (4) As explained above, according to the present invention, theinsolubilized sections are formed primarily by a reaction based onpolarity changes, and therefore it is possible to provide a negativeresist composition with vastly improved sensitivity and resolutionwithout the problem of pattern swelling.

[0485] According to the present invention, there is included analicyclic alcohol with a reactive site that can undergo dehydrationbonding reaction with the alkali-soluble group of the base resin, andtherefore the polarity change is increased when it is added to analkali-soluble polymer, while the molecular weight distribution, orweight average molecular weight, of the sections insolubilized by lightexposure is within a prescribed range, thus making it possible to obtaina negative resist composition with high sensitivity and high resolution.

[0486] According to the present invention, it is also possible to obtaina negative resist composition with high sensitivity and resolution.

[0487] Further, according to the present invention, it is possible toform an even more preferable negative resist composition.

[0488] Furthermore, according to the present invention, it is possibleto obtain resist patterns with high sensitivity and high resolution.

We claim:
 1. A negative resist composition comprising a base resin whichcomprises an alkali-soluble polymer, a photo acid generator which iscapable of decomposing upon absorption of image-forming radiation togenerate an acid, and an alicyclic alcohol with a reactive site that canundergo dehydration bonding reaction with the alkali-soluble group ofsaid base resin in the presence of the acid generated by said photo acidgenerator, in which no more than 10 wt % thereof consists of componentswith a molecular weight of under 2000 in said base resin.
 2. A negativeresist composition according to claim 1, in which said base resincontains a phenol-based compound.
 3. A negative resist compositionaccording to claim 1, in which said alicyclic alcohol has an adamantanestructure.
 4. A negative resist composition according to claim 1, inwhich said alicyclic alcohol has a tertiary alcohol structure with astereochemically fixed structure.
 5. A negative resist compositionaccording to claim 4, in which said tertiary alcohol is a 1-adamantanolor a derivative thereof.
 6. A negative resist composition according toclaim 1, in which said photo acid generator is one selected from thegroup consisting of onium salts, halogenated organic substances andsulfonic acid esters.
 7. A negative resist composition according toclaim 2, in which said alicyclic alcohol has an adamantane structure. 8.A negative resist composition according to claim 2, in which saidalicyclic alcohol has a tertiary alcohol structure with astereochemically fixed structure.
 9. A negative resist compositionaccording to claim 3, in which said alicyclic alcohol has a tertiaryalcohol structure with a stereochemically fixed structure.
 10. Anegative resist composition according to claim 8, in which said tertiaryalcohol is a 1-adamantanol or a derivative thereof.
 11. A negativeresist composition according to claim 9, in which said tertiary alcoholis a 1 -adamantanol or a derivative thereof.
 12. A negative resistcomposition according to claim 2, in which said photo acid generator isone selected from the group consisting of onium salts, halogenatedorganic substances and sulfonic acid esters.
 13. A negative resistcomposition according to claim 3, in which said photo acid generator isone selected from the group consisting of onium salts, halogenatedorganic substances and sulfonic acid esters.
 14. A negative resistcomposition according to claim 4, in which said photo acid generator isone selected from the group consisting of onium salts, halogenatedorganic substances and sulfonic acid esters.
 15. A negative resistcomposition according to claim 5, in which said photo acid generator isone selected from the group consisting of onium salts, halogenatedorganic substances and sulfonic acid esters.
 16. A negative resistcomposition according to claim 8, in which said photo acid generator isone selected from the group consisting of onium salts, halogenatedorganic substances and sulfonic acid esters.
 17. A negative resistcomposition according to claim 7, in which said photo acid generator isone selected from the group consisting of onium salts, halogenatedorganic substances and sulfonic acid esters.
 18. A negative resistcomposition according to claim 7, in which said alicyclic alcohol has atertiary alcohol structure with a stereochemically fixed structure. 19.A negative resist composition according to claim 18, in which saidtertiary alcohol is a 1 -adamantanol or a derivative thereof.
 20. Anegative resist composition according to claim 19, in which said photoacid generator is one selected from the group consisting of onium salts,halogenated organic substances and sulfonic acid esters.